[Index state tracking: Rollout] Add runbook

Background

SRE, on-call and DRI teams need a runbook to help manage the Ai::ActiveContext feature during maintenance tasks, change requests, and incidents

Proposal

• create a new folder ai-active-context (or other appropriate name) in https://gitlab.com/gitlab-com/runbooks/-/tree/master/docs
• create a README.md file in that folder. the format for Advanced search runbook can be used as a guide. we should include the following sections
  • Quick start (how to get to admin page or where configuration lives)
  • How-to guides
    • enable/disable feature
    • pause indexing
    • pause search (is this a thing?)
    • pause the migration worker, using the sidekiq chatops commands is good enough. If they are cron workers they should be dropped (not deferred)
  • Concepts (can link to documentation if it exists). This should be a high level overview of how the feature works. Listing out specific workers or services involved is helpful during incidents for folks not familiar with the code
  • Incident Management. This can be light to start, but should be built upon as incidents occur with mitigation steps.