mgr/volumes: Bump up AuthMetadataManager's version

mgr/volumes: Bump up AuthMetadataManager's version

With ceph_volume_client and mgr-volumes co-existing
for sometime, the version of both needs to be same.
The ceph_volume_client version <=5 can't decode
'subvolumes' key in auth-metadata file. Hence to
handle version in-compatibility, the version of
ceph_volume_client is bumped up to 6 and the same
needs to be done in mgr-volume's AuthMetadataManager

Fixes: https://tracker.ceph.com/issues/49374
Signed-off-by: Kotresh HR <khiremat@redhat.com>