Resolve "Performance bar appears enabled even though it won't show up"

Closes #39570

See merge request gitlab-org/gitlab-ce!15084

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

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

Remove code from global namespace

See merge request gitlab-org/gitlab-ce!15058

Update i18n in FE docs for marking and interpolation

See merge request gitlab-org/gitlab-ce!15020

Fix call stack size exceeded group milestone description autocomplete

Closes #39020

See merge request gitlab-org/gitlab-ce!14972

Merge branch 'pawel/bump_prometheus_gem_to_fix_read_all_values_returning_bad_data-39504' into 'master'

Update Prometheus Gem to fix problem caused by using wrong data offsets

See merge request gitlab-org/gitlab-ce!15081

Changed project select to use it independently and not onlt as a combobutton

See merge request gitlab-org/gitlab-ce!15043

Fix 500 error for old (somewhat) MRs

Closes #36540

See merge request gitlab-org/gitlab-ce!14945

Upgrade Gitaly to v0.50.0

See merge request gitlab-org/gitlab-ce!15050

Merge branch '39054-activerecord-statementinvalid-pg-querycanceled-error-canceling-statement-due-to-statement-timeout' into 'master'

Resolve "ActiveRecord::StatementInvalid: PG::QueryCanceled: ERROR:  canceling statement due to statement timeout"

Closes #39054

See merge request gitlab-org/gitlab-ce!15063

Add docs for backing up to Google Cloud Storage

See merge request gitlab-org/gitlab-ce!15074

Add missing circuitbreaker metrics to prometheus documentation

See merge request gitlab-org/gitlab-ce!15062

* master: (51 commits)
  Move locked check to a guard-clause
  Ci::Build tag is a trait instead of an own factory
  [CE backport] Saved configuration for issue board
  Use the correct project visibility in system hooks
  Add changelog
  more readable changelog
  Make merge_jid handling less stateful in MergeService
  Fetch the merged branches at once
  remove extra whitespace
  use a delegate for `username` to be more future friendly
  Merging EE doc into CE
  add changelog entry
  Avoid using Rugged in Gitlab::Git::Wiki#preview_slug
  Cache commits on the repository model
  Remove groups_select from global namespace & simplifies the code
  Change default disabled merge request widget message to "Merge is not allowed yet"
  Semi-linear history merge is now available in CE.
  Remove repetitive karma spec
  Improve spec to check hidden component
  Rename to shouldShowUsername
  ...

Ci::Build tag is a trait instead of an own factory

See merge request gitlab-org/gitlab-ce!15077

Fix widget of locked merge requests not being presented

See merge request gitlab-org/gitlab-ce!15069

Minor annoyance of mine, and there were a couple of things wrong, for
example:
1. Switching on a property is just a trait
2. It didn't inherrit from its parent

Find and replace through the code based fixed all occurances.

[CE backport] Saved configuration for issue board

See merge request gitlab-org/gitlab-ce!15009

Use the correct project visibility in system hooks

Closes #39496

See merge request gitlab-org/gitlab-ce!15065

grab the correct username when confirming secondary email

Closes #39366

See merge request gitlab-org/gitlab-ce!15010

Remove Autosave class from global namespace

See merge request gitlab-org/gitlab-ce!14856

Update docs on creating MRs

See merge request gitlab-org/gitlab-ce!14982

Fetch the merged branches at once.

Checking it one by one in the view. We don't cache this yet
because this would already much improve the performance.

A naive test against a particularly large repository:

``` ruby
begin
  now = Time.now
  branches.map{ |b| r.merged_to_root_ref?(b.name) }
  Time.now - now
end # 8.265830782
```

Around 10 times faster:

``` ruby
begin
  now = Time.now
  r.merged_branches(branches.map(&:name))
  Time.now - now
end # 0.807405397
```

This should make the branches page usable.

See merge request gitlab-org/gitlab-ce!14729

Move doc/development/ee_features.md to CE

See merge request gitlab-org/gitlab-ce!15066