As part of the work to enable CephFS shallow-copy compatibility with OADP, we must allow for the storage class that VSM uses to be configurable.

This means that even though the source application's PVC is using storage class A, the user may want volumesnapshotmover to use storageclass B for the volsync workflow. This will allow a user to make a copy of their storageclass with `backingSnapshots: true` to be used with data mover and improve performance.