Investigate automating the creation of the Howto index

The following discussion from !1846 (merged) should be addressed:

• @ashmckenzie started a discussion: (+3 comments)

The only idea I have is following a pattern we have elsewhere where we:

• Write a Rake task or similar to take a template and populate it with information based on a heuristic (like things in howto).
• Commit the result (so the folks can read it in raw markdown without any post-processing).
• Have some processing step in the docs pipeline that checks that the Howto index isn't out-of-date (with an error telling you what to run).

Some examples:

• https://docs.gitlab.com/ee/development/rake_tasks.html#update-graphql-documentation-and-schema-definitions
• https://gitlab.com/gitlab-org/gitlab-runner/-/blob/5905c876b6f4a329dab9c1f42d10f816731c086c/docs/configuration/feature-flags.md#L31