Resolve "Verify integrity of repositories"

Adds a rake task that performs git fsck on all repos, including repositories in subgroups and hashed storage.

This also has the side effect of adding subgroup and hashed storage support to the list of gitlab:git:* tasks.

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #40228 (closed)