Investigate utility of Proxmox Backup for UCC

Investigate utility of the Proxmox Backup software for UCC, which should integrate nicely with our Proxmox VE cluster, and provides deduplication and other niceties found in enterprise backup software from this century (courtesy of ZFS). We ultimately need to implement something that backs up all our VMs and ideally everything else as well, rather than just cherry-picked files sitting on NFS. This will give us a much bigger safety net for things like Proxmox VE upgrades, where Ceph stares menacingly at anyone tempted to embark on such a journey.