mgr/dashboard: set mirrored CephFS volumes/grps/subvs without metadata as unmanaged

- Return state unmanaged on getxattr failures
  - Set unmanaged label and disable actions.
  - Set `-` default empty values
  - Add Recreate action when resource is unmanaged

Fixes: https://tracker.ceph.com/issues/79116
Assisted-by: Claude
Signed-off-by: Pedro Gonzalez Gomez <pegonzal@ibm.com>