Offline tool to repair TarMK

We should have a tool to inspect and repair TarMK files in case the repository does not come up due to a corruption in the tar files.

Ideally, the tool could be pointed to an existing backup and use the backup to fix broken binaries (that might have been erroneously been deleted by the DS GC).

Once we have the tool, we could automatically run it after backups and on the failover instance (OAK-1161)