Resolve "Close MRs open for more than 12 months (with a comment welcoming reopening if there is still interest)"

Dry-run:

• close-stale-bugs
• close-stale-merge-requests

Results:

• 156 merge requests meeting vintage without Community contribution

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations => gitlab-com/www-gitlab-com!74005 (closed)
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Week-in-review

Closes #535 (closed)