Glusterfs is still maintained. Please don't drop support!

[uzumo]

With the removal of native support from QEMU, the feasibility of keeping the plugin is gone. It is time for users to focus on the migration as soon as possible.

https://github.com/proxmox/pve-qemu/commit/fa71af3c796c51f68679fa835eeeff2e7094e5e5