Improve SSH database key lookup documentation

Closes #41399

See merge request gitlab-org/gitlab-ce!16048

Resolve "Download menu expands past the fold and doesn't auto size to the bottom height of the browser window"

Closes #41570

See merge request gitlab-org/gitlab-ce!16299

Fix changes dropdown ellipsis working across browsers

Closes #41561 and #41684

See merge request gitlab-org/gitlab-ce!16281

fix example in ci ssh_keys documentation

See merge request gitlab-org/gitlab-ce!16079

Add note about only 20 commits being included in push payload

See merge request gitlab-org/gitlab-ce!16149

Fix the header level for the Changelog Arguments documentation

See merge request gitlab-org/gitlab-ce!16158

Specifies the accepted refs for downloading an archive via the API

Closes #19843

See merge request gitlab-org/gitlab-ce!16222

Update irker documentation to mention an irker bug with key-protected channels.

See merge request gitlab-org/gitlab-ce!16274

Add option to disable commit stats to commit API

Closes #41681

See merge request gitlab-org/gitlab-ce!16309

Fix: remove unnecessary line

Closes #41501

See merge request gitlab-org/gitlab-ce!16289

Closes #41561

Backport authorized_keys

Closes gitlab-ee#3953

See merge request gitlab-org/gitlab-ce!16014

Fixing re-ordering of an issue when dragging it to the bottom a long issue list in the board

Closes #36906

See merge request gitlab-org/gitlab-ce!16250

Remove preview_markdown from the global obj

See merge request gitlab-org/gitlab-ce!16025

Resolve "Pipeline graph uses inconsistent colors for its legend and its content"

Closes #41404

See merge request gitlab-org/gitlab-ce!16260

Backport "Fix environment scope regex" to CE

Closes gitlab-ee#4308

See merge request gitlab-org/gitlab-ce!15945

Save user ID and username in Grape API log (api_json.log)

See merge request gitlab-org/gitlab-ce!16264

Resolve "Install dev dependencies as devDependencies instead of dependencies"

See merge request gitlab-org/gitlab-ce!16288

This will enable admins to identify who actually made the API request.

Relates to #36960

Improve table pagination spec

See merge request gitlab-org/gitlab-ce!16099

Resolve "Timeout is not set for gitaly fetch_remote calls"

Closes #41683

See merge request gitlab-org/gitlab-ce!16245

Refactor dashboard todos inside dispatcher

See merge request gitlab-org/gitlab-ce!16065

The spec for "#add_key does nothing" would always have passed,
since the expectation was on both the wrong object and message.

Originally from branch 'fix-authorized-keys-enabled-default-2738' via merge request https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2240

Removed background migrations which were intended to fix state after using Gitlab
without a default having been set

Squashed commits:
Locally, if Spring was not restarted, `current_application_settings` was still cached, which prevented the migration from editing the file. This will also ensure that any app server somehow hitting old cache data will properly default this setting regardless.
Retroactively fix migration
  This allows us to identify customers who ran the broken migration. Their `authorized_keys_enabled` column does not have a default at this point.
  We will fix the column after we fix the `authorized_keys` file.
Fix authorized_keys file if needed
Add default to authorized_keys_enabled setting
  Reminder: The original migration was fixed retroactively a few commits ago, so people who did not ever run GitLab 9.3.0 already have a column that defaults to true and disallows nulls. I have tested on PostgreSQL and MySQL that it is safe to run this migration regardless.
  Affected customers who did run 9.3.0 are the ones who need this migration to fix the authorized_keys_enabled column.
  The reason for the retroactive fix plus this migration is that it allows us to run a migration in between to fix the authorized_keys file only for those who ran 9.3.0.
Tweaks to address feedback
Extract work into background migration
Move batch-add-logic to background migration
  Do the work synchronously to avoid multiple workers attempting to add batches of keys at the same time.
  Also, make the delete portion wait until after adding is done.
Do read and delete work in background migration
Fix Rubocop offenses
Add changelog entry
Inform the user of actions taken or not taken
Prevent unnecessary `select`s and `remove_key`s
Add logs for action taken
Fix optimization
Reuse `Gitlab::ShellAdapter`
Guarantee the earliest key
Fix migration spec for MySQL

See merge request gitlab-org/gitlab-ee!3323

Backported as part of authorized_keys in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16014

Backport to CE, originally branch 'evn-ssh-clarify-docs

See merge request gitlab-org/gitlab-ee!3753