fix shibboleth misconfigurations resulting in authentication bypass

This merge request fixes #22267 where a misconfigured Shibboleth `HTTP_UID` or `HTTP_EPPN` could result in users being logged into an account that did not belong to them.

See merge request !7428

Fix issue where "Without projects" filter admin area shows 0 users incorrectly. Before this fix, if any outstanding group or project invitations exist the count show as 0.

Fixes #3367

See merge request !6611

Allow commit note to be visible if repo is visible

## What does this MR do?

It enforces the `:download_code` permission in `Event#visible_to_user?` for commit notes.

Closes #23824

See merge request !7504

Stopped multiple requests with dropdowns

## What does this MR do?

Fixes an issue where the user dropdown would send 2 requests when the user opens the dropdown.

## What are the relevant issue numbers?

Closes #24131

See merge request !7505

Fixed issue boards counter border when unauthorized

## What does this MR do?

When the user is unauthorized & view issue boards, the border on the counter will not be the whole way around. This fixes that. 

## Screenshots (if relevant)

![Screen_Shot_2016-11-16_at_13.03.36](/uploads/54d97f7f4114044aad3bdc78961a31c8/Screen_Shot_2016-11-16_at_13.03.36.png)

## What are the relevant issue numbers?

Closes #23664

See merge request !7501

Defer saving project services to the database if there are no user changes

## What does this MR do?

It defers saving project services to the database as long as it is possible. It creates a project service when creating a project only if this project service has an active template. After that project services are saved on the first edit.

## Are there points in the code the reviewer needs to double check?

- tests that used `build_missing_services` before the change
- number of queries executed

## Why was this MR needed?

Motivation in #22281

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Fixes #22281

See merge request !6958

Search for a filename in a project

Closes #23117

See merge request !7426

Opening the user dropdown currently sends 2 requests. This has been changed so only one is sent

Closes #24131

Disable the "request access" functionality by default for new groups and projects

Currently this feature is enabled by default, and additional action is required to disable it.

Closes #21992 
Closes !7011

See merge request !7425

Signed-off-by: Rémy Coutable <remy@rymai.me>

Fix UX Guide link on Contributing.md

Current link on the CONTRIBUTING.md page was to the old UI Guide. This should be updated to the new link.

See merge request !7493

Move 'Explore Snippets' Spinach feature to Rspec

## What does this MR do?
It moves the `features/snippets/discover.feature` Spinach test to a Rspec feature.

## Are there points in the code the reviewer needs to double check?
The original feature was called 'Discover Snippets', but the UI no longer reflects this wording. The new Rspec feature is called 'Explore Snippets' to reflect UI/Controller/View naming in use.

## Why was this MR needed?
As part of deprecating the Spinach test suite.

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [-] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [-] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [-] API support added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
#23036

See merge request !7349

Do not create a MergeRequestDiff record when source branch is deleted

Fixes #23413 
Fixes #23897

See merge request !7481

Limit labels returned for a specific project as an administrator

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/24527

See merge request !7496

Use setter for key instead AR callback

## What does this MR do?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- n/a [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- n/a API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6763

See merge request !7488

fix labels API adding missing parameter (current_user)

See merge request !7458

Fix a badly-performing migration

See merge request !7483

Move 'Search Snippets' Spinach feature to Rspec

## What does this MR do?
Moves the Spinach feature `features/snippet_search.feature` to an RSpec feature `spec/features/snippets/search_snippets_spec.rb`.

## Are there points in the code the reviewer needs to double check?

The search results page URL was being visited directly in the original Spinach test, using an encoded search query and specific parameters to trigger the snippet searches. I have changed the RSpect feature to fill in the search box on the snippets dashboard page to retrieve results to cover the missing test coverage on the search box and to avoid the feature test from relying on the implementation details of the search URL structure.

## Why was this MR needed?

As part of deprecating the Spinach test suite.

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [-] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [-] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [-] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

#23036

See merge request !7494

Improved redis sentinel documentation

## What does this MR do?
Updates Redis Sentinel documentation (most Omnibus stuff).

## Are there points in the code the reviewer needs to double check?
Grammar / Documentation

## Why was this MR needed?
After this https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests/1000 get merged, people will need to follow new instructions.

## Checklist

- Documentation follows Sentinel best-practices:
  - [x] Suggests amount of sentinel nodes
  - [x] Suggests amount of redis nodes
  - [x] Suggests quorum value according to recomended amount of sentinel nodes
  - [x] Describes how to define quorum according to best-practices
  - [x] Lists ports and firewall checklist
- [x] Following Documentation bring us to a working environment
- [ ] Documentation is clear and have no gramatical issue

## What are the relevant issue numbers?

gitlab-org/omnibus-gitlab#1565

See merge request !6471

Prior, an administrator viewing a project's Labels page would see _all_
labels from every project they had access to, rather than only the
labels of that specific project (if any).

This was not an information disclosure, as admins have access to
everything, but it was a performance issue.

When unauthorized the border on the counter in issue boards didn't span the whole way around

Closes #23664

[ci skip]

[ci skip]

Navigation bar issuables counters reflects dashboard issuables counters

Adds a 2 minute cache on navigation bar issuables counters.

The counters on dashboard/issues and dashboard/merge_requests are cached while the navigation bar issuables counters were not. Users read incoherent issuables count throughout the application.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/23882

See merge request !7368

Remove gitattribute entry for CHANGELOG.md

This should no longer be necessary now that we've got automatic changelogs!

See merge request !7479

Limit autocomplete to currently selected items

When using the /unlabel command the autocomplete list of labels is now
limited to the list of labels currently assigned to the issue.

Closes #22680

See merge request !6796

[ci skip]

In order to have a valid MergeRequestDiff record when need head_commit_sha.
When a source branch is deleted head_commit_sha is nil.
This causes an exception in merge request "Changes" tab.