Single sign-on console access for the hypervisor and backup hosts

Console access for the Proxmox hosts and the backup server now goes through single sign-on, so the hypervisors and backup server are reachable from anywhere without a VPN instead of by raw address on the local network only.

The out-of-band console proxies were also renumbered so each label matches the machine it actually manages. Previously the numbering had drifted: a console labelled for one server opened another, which is a poor property for the tool you reach for when a machine is down.

Five management endpoints belonging to the retired virtualization platform were removed, along with their DNS records and sign-on configuration.

Tracking post for the changelog entry covering this work.