安装Upgrade ProxMox VE from 6.4 to 7.0

NOTE: These steps are for a single standalone ProxMox server. They have not been tested in a clustered environment

NOTE: Make sure to create external backups of all important VMs and CTs just in case something goes wrong. You've been warned.

Source and Additional Info: https://pve.proxmox.com/wiki/Upgrade_from_6.x_to_7.0