Add processor to remind MR author MWPS is not compliant

What does this MR do and why?

Closes #1057 (closed)

When an MR is merged by the author, GitLab bot posts a reminder comment that this is not a compliant action.

Expected impact & dry-runs

See comments below for example of this reminder comment

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