Processing Commits Using Sidekiq

What does this MR do?

This moves the code of GitPushService#process_commit_messages into a separate Sidekiq worker. This allows processing of commits to happen in parallel, speeding up the process. See the individual commit (messages) for more information.

Are there points in the code the reviewer needs to double check?

As far as I could tell/test the behaviour is the same as before (logic wise), but an extra pair of eyes on this would be appreciated.

Why was this MR needed?

Processing commits in sequence is hella slow, especially when commits mention a lot of issues.

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/15463