How to install M.2 SSD in HP G2 800 Mini

As part of my strategy to not worry about the slightly dodgy SMART reporting on the SDD’s in my HP Elitedesk G2 800 Mini Proxmox nodes, I’d decided to make use of the full sized M.2 slot to install 256GB NVME drives. That way I can boot from those, and have the SSD’s running ZFS which allows scrubbing to check the integrity of all the data. My VM disks can live on this drive.