Move *-nvidia image build workflow into main repo

[bsherman]

Now that nvidia has removed the building of the nvidia kmod in favor of a build from akmods, we can easily migrate the building of *-nvidia images into this repo as a job that runs after successful *-main builds.

[castrojo]

This is going to be so cool, the efficiency benefits on real builders will be awesome!

[EyeCantCU]

This is a great idea. I'll work on this first thing tomorrow