Make the Community contribution workflow more consistent

What does this MR do and why?

Implementation of https://gitlab.com/gitlab-com/quality/contributor-success/-/issues/97.

Closes https://gitlab.com/gitlab-com/quality/contributor-success/-/issues/87, #1006 (closed).

This new workflow is documented by gitlab-com/www-gitlab-com!104914 (merged). Check out specifically the diagram that describes the new workflow at https://rymai-master-patch-73615.about.gitlab-review.app/handbook/engineering/quality/contributor-success/index.html#community-merge-request-workflow-automations.

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.

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