Merge remote-tracking branch 'origin/refactor-clusters' into 36629-35958-add-cluster-application-section

Merge remote-tracking branch 'origin/38464-k8s-apps' into 36629-35958-add-cluster-application-section

Resolve "Expose project visibility as CI variable"

Closes #37473

See merge request gitlab-org/gitlab-ce!15193

Fix a migration that adds merge_requests_ff_only_enabled column to MR table

Closes #39382 and #39357

See merge request gitlab-org/gitlab-ce!15195

Replace PhantomJS with Headless Chrome for GitLab Integration Tests

Closes #30876

See merge request gitlab-org/gitlab-ce!12244

Fix clusters description text collapsing away on page-load

Closes #39771

See merge request gitlab-org/gitlab-ce!15177

* master: (33 commits)
  Ignore SQL CACHE hits in Sherlock
  Fix SQL timings for the performance bar
  Find the LFS-objects for a fork within a the fork network
  Remove bottom-border from last responsive table row
  Add system hooks user_rename and group_rename
  Unlink a project from a fork network when it's source was deleted.
  Make sure the settings page renders when root of a fork is deleted
  Remove Peek's original keyboard shortcut (numpad 0, keycode 96)
  Add application setting to Auto DevOps docs
  Enable MergeableSelector in scss-lint (for !14567)
  Enable MergeableSelector in scss-lint (for !14055)
  Enable MergeableSelector in scss-lint (for !14062)
  Enable MergeableSelector in scss-lint (for !14398)
  Enable MergeableSelector in scss-lint (for !13480)
  Enable MergeableSelector in scss-lint (for !13473)
  Enable MergeableSelector in scss-lint (for !13600)
  Enable MergeableSelector in scss-lint
  Resolve ""To do" should be "Todos" on Todos list page"
  Avoid regenerating the ref path for the environment
  Remove white space at bottom of issue boards
  ...

Fix Gitlab::Metrics::System#real_time and #monotonic_time doc

See merge request gitlab-org/gitlab-ce!15187

Render 404 when polling commit notes without having permissions

Closes #39176

See merge request gitlab-org/gitlab-ce!15140

Pull tags from true origin

See merge request gitlab-org/gitlab-ce!15100

[ci skip]

Resolve "Auto DevOps application setting is not documented"

Closes #38500

See merge request gitlab-org/gitlab-ce!15170

Ignore SQL CACHE hits in Sherlock

See merge request gitlab-org/gitlab-ce!15182

Remove bottom-border from last responsive table row

Closes #39776

See merge request gitlab-org/gitlab-ce!15179

Fix SQL timings for the performance bar

See merge request gitlab-org/gitlab-ce!15181

This fixes some bugs related to forked projects of which the source was deleted.

Closes #39667

See merge request gitlab-org/gitlab-ce!15150