Verify integrity of repositories

In disaster recovery scenarios where customers are relying on GitLab to replicate and sync their data to a different location it would be nice to have a rake task to verify the integrity of repositories.

Same as uploaded files (https://gitlab.com/gitlab-org/gitlab-ce/issues/39949):

Bit rot or other problems (e.g., corruption during a Geo primary -> secondary file sync) could cause corruption of the file.

Proposal

• Add a git fsck (or similar) task to verify the integrity of local repositories

Out of scope:

• GCP scenarios (not on local disk)