Improve weekly community contributions report

What does this MR do and why?

Improves the weekly community contribution report by:

1. Removing a non actionable section of the report
2. Rewording section headings to be more explicit
3. Adding numbering to the merged MRs table

Expected impact & dry-runs

Dry-run - https://gitlab.com/gitlab-org/quality/triage-ops/-/jobs/2172583235

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