PXE Server Setup, PXE Image building

[finchd]

Next step to getting this project more regular updates: needs a build server.
I could try to use a cloud service, but testing OS install steps there is pretty difficult.
Instead, I'll add a PXE server role/playbook here, and run that against one IoT board.
A second playbook should generate bootable images that slipstream this repo into the latest arch install iso.
With both in place, I can boot a second target ARM board.
That won't test things like KVM or GPU driver compatibility, but those I'm only going to catch once my daily-driver desktop isn't Windows...