MR author can set MWPS

What does this MR do and why?

• This was added here !1499 (merged)
• This was a first step for a compliance change: "The ultimate goal of this control is to evidence that it’s not technically feasible for a single person to be able to make a production change. ."
• It is not possible to approve an MR where you added one more more commits, so this goal has already been accomplished.
• Enabling MR authors to set MWPS on MRs with all necessary approvals is more efficient. Currently, folks are often asking in Slack for others to set MWPS because the last approver forgot.
• If we move forward, we should also comment on https://gitlab.com/gitlab-org/gitlab/-/issues/366696+

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-policies-with-a-dry-run on how to perform dry-runs for new policies.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/blob/master/doc/reactive/best_practices.md#use-the-sandbox-to-test-new-processors on how to make sure a new processor can be tested.

Action items

• If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• (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