Streamline image building using buildah

Right now our image building process is specifically assuming Minikube as loads it into this directly. We should replace this podman build with buildah directly. This has several advantages:

• We can build the image from inside the build pod, so no need for copying RPMs all over the place.
• We can push to a registry of our choice.

Especially the second point makes this agnostic to the Kubernetes setup as we can configure it to push to any registry we want. That makes this very flexible. It also reduces the amount of work done on the host machine; we just need to make sure that build image has buildah available.

I will wait for !765 (merged) to be merged, as this brings a few nice things with it.