Automatically assign the most relevant coach based on group label

What does this MR do and why?

Depends on !1455 (merged).

• When workflowready for review is added

  • If the MR has reviewers set, ask them to review or reassign:

    

  • If the MR doesn't have any reviewers, assign for review the most relevant MR coach based on the group label (i.e. find a coach from that group), or fallback to a random coach:

    

Expected impact & dry-runs

These are strongly recommended to assist reviewers and reduce the time to merge your change.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-with-a-dry-run on how to perform dry-runs.

Closes #1039 (closed).

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review