Add accept-dataloss sub-command

Adds 'accept-dataloss' sub-command which allows designating a new authoritative storage for a repository. This might be necessary if a repository is in read-only mode and recovering the data is not viable. The current version of the repository on the authoritative storage is considered latest and versions on the other physical storages will be overwritten with it.

This adds a new command, I'll follow up with an MR to remove the old virtual storage scoped implementation.