Add a runbook for monitoring SAST vulnerability auto resolution

Why is this change being made?

This merge request updates the Static Analysis handbook page to:

1. Add a new runbooks section.
2. Add a new runbook: "How to monitor and respond to issues with SAST Automatic Vulnerability Resolution?".
3. Fix a typo in the page.

Please note: the runbook is added to the handbook, as discussed with @theoretick due to the lack of centralized commonplace for Secure stage runbooks, and because we felt this isn't suitable for docs.gitlab.com either, but I'd be happy to move this somewhere else.

Author Checklist

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