Reorganize main builds to better support image flavors: main, nokmods, nvidia, asus, surface

[bsherman]

We previously completed #313 which merged *-nvidia image workflow into this main repo. But since then, we've noticed some excessive build times and duplication of builds due to the chained nature of main+nvidia builds. Additionally, we have some new build workflow needs as we are trying to support various laptop types, specifically: asus, framework, and surface.

To better handle the new situation we plan to do the following:

1. restore the nvidia repo and once again build *-nvidia images there, removing the *-nvidia complexity from main workflow (the nvidia kmods will still be built in akmods repo)
2. modify main repo workflow adding a *-nokmods image flavor for all variants (silverblue, kinoite, etc) which will not include any kmods from our akmods repo
3. asus and surface downstream images will start building FROM ghcr.io/ublue-os/VARIANT-nomods which will allow them to use custom kernel and kmods.
4. Create build matrix to support distinct builds for kernel variants akmods#68

End states:

1. Effectively *-nokmods will be the foundational image from which *-main, *-asus, and *-surface are built.
2. Downstream image builds currently using *-main will not see a change (including *-nvidia, bluefin and bazzite)

[bsherman]

Welp. That was quick.

This looks to be wrapped up except for point 4 which has it's own ticket: ublue-os/akmods#68

@castrojo @KyleGospo @EyeCantCU