Support qcow data-file for Ceph storage

### The required feature described as a wish

As a User/Admin/Operator I would like to have support for the `data-file` functionality of libvirt 10.10 supported on newer hosts. This way one would be able to use a lot of different backup solutions such as virtnbdbackup to back up VMs running on a Ceph primary storage.

https://www.mail-archive.com/devel@lists.libvirt.org/msg07367.html

> * qemu: Support for the 'data-file' QCOW2 image feature
>
> The QEMU hypervisor driver now supports QCOW2 images with 'data-file'
feature present (both when probing form the image itself and when specified
explicitly via ```` element). This can be useful when it's
required to keep data "raw" on disk, but the use case requires features
of the QCOW2 format such as incremental backups.

There are probably a lot of things to take into account, but it would still be a great improvement.

Commencez par lire la description référencée de la fonctionnalité data-file de libvirt 10.10 et retracez la manière dont CloudStack gère les images QCOW2 sur le stockage primaire Ceph. Identifiez les points d’entrée storage et hypervisor concernés ainsi que les tests existants ; le travail est considéré comme terminé lorsque les hôtes plus récents peuvent utiliser des images QCOW2 data-file pour des VMs reposant sur Ceph sans perturber la gestion existante des images.

Rédigé par le modèle d'indexation à partir du texte de l'issue.