Revert the "accurate issuable counts in issuable list" feature

## Why was this MR needed?

!6455 introduced a performance killer, so we revert it until we find a proper solution that's not killing performance.

## What are the relevant issue numbers?

Revert !6455 and !4960.

See merge request !6476

Describe how the recent changes of CI permissions affect builds

## What does this MR do?

This describes how the CI permission changes

See merge request !6451

[ci skip]

- Add link to external user
- Move build triggers up

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

[ci skip]

fix dropdowns for mr-versions

## What does this MR do?
Change markup of mr version dropdowns to be in line with ui guidelines so that the dropdown content is scrollable.

## Why was this MR needed?
Dropdowns were not scrolling.

## Does this MR meet the acceptance criteria?

- [ ] [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
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] 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)
- [ ] [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/issues/21427

cc @brycepj @dzaporozhets

See merge request !6460

Intercept issues search form submit to preserve filters.

## What does this MR do?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/896 by intercepting manual search form submission and redirecting it to use existing logic (now factored out into `executeSearch`).  

## Why was this MR needed?

Manual form submission (keying in 'enter') in issues search did not preserve applied filters. 

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/896

See merge request !6054

Fixes protected branches not removing active item

## What does this MR do?

Fixes an problem where protected branches weren't getting their active item removed on a second click because they dont have a field value.

## Why was this MR needed?

Protected branches could not have their clicked items removed once clicked.

See merge request !6440

[ci skip]

Revert "Merge branch '22421-fix-issuable-counter-when-more-than-one-label-is-selected' into 'master'"

This reverts commit 8ed5be59, reversing
changes made to fb0d1378.

API: Return 404 when trying to fork to unaccessible namespace

Closes #22417

See merge request !6452

Fix pipeline error when trying to read empty merge request diff

When a user pushed something which resulted an empty merge request diff, `st_commits` would be `nil`. Therefore we also need to check if there exists `st_commits`.

We could tell this from:

``` ruby
def commits
  @commits ||= load_commits(st_commits || [])
end
```

and

``` ruby
def save_commits
  new_attributes = {}

  commits = compare.commits

  if commits.present?
    commits = Commit.decorate(commits, merge_request.source_project).reverse
    new_attributes[:st_commits] = dump_commits(commits)
  end

  update_columns_serialized(new_attributes)
end
```

Closes #22438

See merge request !6470

Fixups for Frontend for Merge Request Diff

## What does this MR do?

Makes a few revisions to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6343, as per feedback from @DouweM. Specifically, it removes a duplicate in the changelog, removes colons in dropdowns, uses icon helper, and fixes the 'Show original' link path.

## Why was this MR needed?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6343 was already merged and this is a needed patch. 

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6343

See merge request !6448

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

Update merge request versions documentation with new screenshots

For #13570 based on https://gitlab.com/gitlab-org/gitlab-ce/issues/21427

See merge request !6454

Hotfix the issuable counters when filtering by multiple labels

This is an ugly fix, but it make the counters work when multiple labels are selected so I think we should include it in 8.12, and try to find a proper fix afterward.

Closes #22421

See merge request !6455

Update db/schema.rb per most recent migrations



See merge request !6446

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6470#note_15856755

Bump gitlab-shell upgrade version to 3.6.0 for 8.12

[ci skip]

Closes #22442

See merge request !6469

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

(Also removes duplicate changelog entry.)

Closes #22438

[ci skip]

Fix typos in cycle analytics docs



See merge request !6467

[ci skip]

Change location and refactor issue closing pattern documentation

## Moving docs to a new location?

See the guidelines: http://docs.gitlab.com/ce/development/doc_styleguide.html#changing-document-location

- [x] Make sure the old link is not removed and has its contents replaced with a link to the new location.
- [x] Make sure internal links pointing to the document in question are not broken.
- [x] Search and replace any links referring to old docs in GitLab Rails app, specifically under the `app/views/` directory.
- [x] If working on CE, submit an MR to EE with the changes as well.

See merge request !6466

Split into user and administrator docs:

- administration/issue_closing_pattern.md
- user/project/issues/automatic_issue_closing.md

[ci skip]

This reverts merge request !6429

Reorganize sections in Admin area settings

## What does this MR do?

Some settings were under the "wrong" category. This is an attempt to provide proper categories and move relevant settings there.

## What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/20126


See merge request !5449