[Feature] Add support for different VM storages

Libvirt has support for [several different storage methods](https://libvirt.org/storage.html) to allow for persistent workloads, and it would be useful to be able to utilize that in this driver. In our usecase, we use a home-built libvirt driver to host user VMs on our nomad cluster, storing them as Ceph RBDs for persistency, though the developer that developed the driver originally is no longer around and we're looking for a replacement.

Sort of similar note to https://github.com/hashicorp/nomad/issues/10053

Start by reading the libvirt storage methods linked in the issue and inspecting the driver's existing VM and storage entry points. Define which storage backends, including Ceph RBD, are in scope and how persistence should be verified; the issue names no files or tests, so those must be located before implementation.

Written by the indexing model from the issue text.