In stage_id backgrond migration.

Merge remote-tracking branch 'origin/active-record-each-batch' into fix/gb/stage-id-reference-background-migration

* origin/active-record-each-batch: (59 commits)
  Added EachBatch for iterating tables in batches
  Extend MR tabs a bit to cover up the avatar holder and collapse icon on scroll
  Update VERSION to 9.4.0-pre.
  Add CHANGELOG
  Fix some N+1 queries in the GET /projects API
  Don't show auxiliary blob viewer for README when there is no wiki
  Improve & fix the performance bar UI and behavior
  Remove orphaned haml files
  Fixed CHANGELOG.md for 9.3.4 release
  Add table for merge request commits
  34727 Remove two columned layout from project member settings
  Just draw :legacy_builds
  Re-enable polling for environments
  Cleanup minor UX issues in the performance dashboard
  Upgrade GitLab Workhorse to v2.3.0
  Added test for the chart legend
  Use correct field for label name, fix default for unit to be blank
  Fix shorter route helpers in production environment
  Encode certificate-authority-data in base64
  Revert "Merge branch 'winh-mr-widget-no-pipeline' into 'master'"
  ...

This module provides a class method called `each_batch` that can be used
to iterate tables in batches in a more efficient way compared to Rails'
`in_batches` method. This commit also includes a RuboCop cop to
blacklist the use of `in_batches` in favour of this new method.

Update VERSION to 9.4.0-pre.

See merge request !12702

Extend MR tabs a bit to cover up the avatar holder and collapse icon on scroll

Closes #34153

See merge request !12589

Don't show auxiliary blob viewer for README when there is no wiki

Closes #34732

See merge request !12689

Upgrade GitLab Pages to v0.5.0

See merge request !12625

Fix some N+1 queries in the GET /projects API

Closes #33748

See merge request !12679

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