mgr/volumes: Update the 'volumes' key to 'subvolumes' in auth metadata file

mgr/volumes: Update the 'volumes' key to 'subvolumes' in auth metadata file

The older auth metadata files created by CephVolumeClient stores the
authorized subvolumes using the 'volumes' key as the notion of
'subvolumes' brought in by mgr/volumes. Hence, this would be tranparently
updated to 'subvolumes' and newer auth metadata files would store them
with 'subvolumes' key.

Also fails the deauthorize if the auth-id doesn't exist.

Fixes: https://tracker.ceph.com/issues/44931
Signed-off-by: Kotresh HR <khiremat@redhat.com>