Draft: Migrate priority::4 to priority::3

What does this MR do and why?

This one-off MR migrates all open/closed/merged issues & MRs from priority4 to priority3 as proposed in gitlab-com/www-gitlab-com#14473.

Expected impact & dry-runs

• migrate-priority4-to-priority3:gitlab-org:dry-run: https://gitlab.com/gitlab-org/quality/triage-ops/-/jobs/3784589763
  • 2669 opened issues
  • 5132 closed issues
  • 15 opened MRs
  • 160 closed MRs
  • 1215 merged MRs
  • 12 opened epics
  • 3 closed epics
• migrate-priority4-to-priority3:gitlab-com:dry-run: https://gitlab.com/gitlab-org/quality/triage-ops/-/jobs/3784589771
  • 48 opened issues
  • 597 closed issues
  • 0 opened, 0 closed MRs
  • 5 merged MRs
  • 1 opened epic
  • 2 closed epics

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