In pvcBackupItemAction.Execute, call GetActionParameters to extract the
snapshotClass from the matched volume policy and pass it through
getVolumeSnapshotReference and createVolumeSnapshot to
GetVolumeSnapshotClass. This connects the volume policy parameter to
the CSI snapshot creation path.
Fixes#8807
Signed-off-by: Shubham Pampattiwar <spampatt@redhat.com>