sctool backup delete doesn't work if cluster is removed

[karol-kokoszka]

Sctool provides CLI to delete snapshots.
It's sctool backup delete https://manager.docs.scylladb.com/stable/sctool/backup.html#backup-delete

The problem is that it doesn't work if the cluster is not managed by Scylla-Manager anymore.

➜  scylla-manager git:(branch-3.2) ./sctool backup delete -c ab667845-996e-46a5-9699-9c3b3c792443 --snapshot-tag sm_20240321143455UTC
Error: get resource: load cluster "ab667845-996e-46a5-9699-9c3b3c792443": not found
Trace ID: L57nt7cMS6mzSJI3qDaKNw (grep in scylla-manager logs)

It makes no sense.
There must an option to just clean the backup location.

GOAL
Let sctool backup delete to remove snapshots of clusters that are not managed by current instance of scylla-manager.