Merge branch 'fix/gb/stage-id-reference-background-migration' into backstage/gb/migrate-stages-statuses

* fix/gb/stage-id-reference-background-migration: (22 commits)
  Reduce a delay between stage_id scheduled migrations
  Improve exception description in bg migrations
  Do not override original AR5 batching interface
  Sanitize id value passed to async background migration
  Improve code examples in background migrations docs
  Add description to exception in bg migrations worker
  Do not compare float with integer in migrations specs
  Improve readability of build stage id migration query
  Use integers to schedule delayed background migrations
  Test if argument passed to a migration is present
  Make `inline` a default sidekiq testing processing again
  Improve specs for background stage_id ref migration
  Perform stage_id ref backgound migration in bulks
  Remove unused background migrations matcher
  Use ActiveRecord 5 batching to schedule bg migration
  Make it possible to schedule bg migrations in bulk
  Add specs for delayed stage_id background migrations
  Schedule background migration only when it is needed
  Find builds that require a migration in batches
  Update `db/schema.rb` with a new schema version
  ...

We still didn't migrate `ci_builds.stage_id`, so we can't use a
belongs_to association. We also have `ci_builds.stage` string attribute,
that we need to phase out in favor of `ci_stages.name`.

Only verifies top position after the request has finished to account for errors

See merge request !12559

Cleanup codeclimate.json file generated by CI

See merge request !12565

Fix 'New merge request' button for users who don't have push access to canonical project

See merge request !12560

Merge branch '34502-gitlab-git-hook-should-set-the-gl_repository-environment-variable' into 'master'

Set the GL_REPOSITORY env variable on Gitlab::Git::Hook

Closes #34502

See merge request !12572

updated version of issues baord images (doc)

See merge request !12558

Render add-diff-note with server and optimize styles

See merge request !12103

Fixed sidebar not collapsing on merge request in mobile screens

Closes #32759

See merge request !12489

Backport changes to Projects::IssuesController and the search bar

See merge request !12551

bugfix: use `require_dependency` to bring in DeclarativePolicy

Closes #34532

See merge request !12571

Resolve "Select branch dropdown is too close to branch name"

Closes #34349

See merge request !12515

Perform unzip quietly in UpdatePagesService

Closes gitlab-ee#225

See merge request !12539

Fixed new navgiation bar logo height in Safari

See merge request !12563

Fix scroll flicker

Closes #34407

See merge request !12501

Defer project destroys within a namespace in Groups::DestroyService#async_execute

See merge request !12435

Clean up issuable lists

Closes #26818

See merge request !11991