Consider a custom GH runner image for bootc systems

https://github.com/orgs/github/projects/4247?pane=issue&itemId=88044286&issue=github%7Croadmap%7C1019

One of the problems we experienced in universal blue over the years is that waiting for the podman stack to be updated in ubuntu runners on github is maddening. When I heard of this feature I thought of an ubuntu-cloud base image, then add the PPAs for podman, buildah, and whatever you need to make a bootc-enabled OS.

And then that's it. This would alleviate some problems:

- We need access to those podman suite features, everything depends on that stack being up to date.
- We're running out of room on github runners, especially nvidia, this would give bootc-on-github orgs more breathing room
- The space saving actions do add minutes to each build, this way would be much faster for everyone.

It'd be awesome to host that here in the upstream repo. It's not GA yet so I'm filing this in the idea factory for now. Or this might make more sense in a podman org? We also don't know how it works in practice so this is more of an aspirational issue. 😄