Interpolate number of MRs merged in title

What does this MR do and why?

1. Makes MR links in the merged section clickable
2. Adds missing pound in merged MR title

Expected impact & dry-runs

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

Action items

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