Improve weekly community merge requests report

What does this MR do and why?

• Split runner merge requests out
• Change idle definition to 3 weeks (from 4)
• Include leading organization label

Expected impact & dry-runs

https://gitlab.com/gitlab-org/quality/triage-ops/-/jobs/3812750813

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