Add more context to production deployment docs

What does this MR do and why?

Preventive action from the postmortem at #1178 (comment 1201846600).

• Add more context around the production deployment of triage-ops.
• Explain the deployment process
• Link to the triage-ops RUNBOOK
• Add a table of contents

Read the rendered markdown.

Expected impact & dry-runs

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

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-with-a-dry-run on how to perform dry-runs.

Action items

• (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