Crosslink changes process for stages/groups

What does this MR do and why?

Part of the Follow-ups when working on a recent stage/group/category changes.

This MR links to the main process that the Product division follows.

Expected impact & dry-runs

None. Documentation changes.

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