Add flag to ignore unreplicated keyspaces during repair

When a repair is triggered on a node in 'dc2' for a keyspace with replication factor

we just ignore the repair in versions < 3. In 3.0+ we fail the repair to make sure the operator does not think the keyspace is fully repaired.

There might be tooling that relies on the old behaviour though, so we should add a flag to ignore those unreplicated keyspaces