Implement lazy popen so LfsChanges doesn't have to wait for rev-list to complete

See merge request gitlab-org/gitlab-ce!15180

CE repository mirroring changes backport

See merge request gitlab-org/gitlab-ce!15184

This allows input to start processing immediately without waiting for the process to complete.
This also allows long or infinite inputs to be partially processed,
which will termiate the process when reading stops with SIGPIPE.

Added discussion_line_code value to note response and use it to query the right…

Closes #38677

See merge request gitlab-org/gitlab-ce!14981

Merge branch 'fix/sm/37299-environments-validate-uniqueness-on-url-and-can-cause-silent-deployment-failures' into 'master'

Remove unique validation from external_url in Environment

Closes #37299

See merge request gitlab-org/gitlab-ce!15202

Fix cron_parser_spec.rb (`master` branch failure on Nov 5th)

Closes #39817

See merge request gitlab-org/gitlab-ce!15196

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

Enable MergeableSelector in scss-lint

See merge request gitlab-org/gitlab-ce!12810