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.

Comece lendo a descrição referenciada do recurso data-file do libvirt 10.10 e rastreando como o CloudStack lida com imagens QCOW2 no armazenamento primário Ceph. Identifique os pontos de entrada de storage e hypervisor envolvidos e os testes existentes; o trabalho estará concluído quando hosts mais novos puderem usar imagens QCOW2 data-file para VMs apoiadas por Ceph sem quebrar o tratamento existente de imagens.

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