Cache only apt and ruby from vendor

## What does this MR do?

Optimises caching mechanism when testing gitlab-ce/ee repositories.


See merge request !4619

Instrument all Banzai::ReferenceParser classes

## What does this MR do?

This MR instruments all the classes in the `Banzai::ReferenceParser` namespace.

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

No.

## Why was this MR needed?

The classes in question weren't instrumented meaning we have no idea how they're performing in production.

## What are the relevant issue numbers?

None.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- [ ] ~~Tests~~
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4620

Add guide on changing a document's location

## What does this MR do?

Add a documentation styleguide when changing a document's location.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/3349


See merge request !4624

Change to new Notes styleguide



See merge request !4625

[ci skip]

[ci skip]

Fix migration helper race conditions

## What does this MR do?

This MR fixes two problems with the migration helpers:

1. An error in `change_column_null` would not drop the previously created column
2. `update_column_in_batches` would rely on the number of rows in a table to determine how many to update. This meant that newly inserted rows (after the `COUNT`) would not be taken into account.

This MR also removes an outdated comment for `update_column_in_batches`.

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

No.

## Why was this MR needed?

See above.

## What are the relevant issue numbers?

Fixes #18483

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [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
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4618

Only show branches for revert / cherry-pick

## What does this MR do?

Stop showing tags in the revert and cherry-pick select options. You can't change a tag anyway.

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

Uncertain.

## Why was this MR needed?

Showing tags doesn't make any sense and will just throw an exception if the user tries to cherry-pick or revert onto a tag.

## What are the relevant issue numbers?

Fixes #18377.

## Screenshots (if relevant)

On the GitLab CE repo:

![image](/uploads/9c5a6f09300a7c46d0a794bef2956992/image.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry 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 [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4596

Change logs.md location in README

## What does this MR do?

Forgotten link from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4622

See merge request !4623

Move logs/logs.md to administration/logs.md

## What does this MR do?

Move `logs.md` documentation under `administration/` where it fits better.

## Why was this MR needed?

For a better doc structure.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/3349

See merge request !4622

[ci skip]

Remove notification level from user model

part of #3359 

See merge request !4494

[ci skip]

Tags are immutable, so we can't add a commit to either revert or
cherry-pick another commit to them.

Now that this code is no longer part of Banzai::Filter it needs to be
instrumented explicitly.