Refactor image building (e.g. using Buildah instead of Docker)

[n-thumann]

What

This PR

• changes Docker with Podman / Buildah to build, test and push our images (fixes currently broken workflow)
• disables updating of images by default
• includes the registry in the baseimage name
• pins our workflow dependencies.

Why

Docker dropped support for Docker Image Format v1 and Docker Image manifest version 2, schema 1. Old images, like we are depending on in this repo, are still using those deprecated versions though. Buildah / Podman still have support for those.
If those older images are converted to version 2, schema 2 at some point, we could go back to Docker.

I also disabled the updating of images by default. My intention back then was to provide mostly up-to-date images, but we actually want rather non-update / vulnerable images in this repo. Besides that, updating the images lead to build issues in the past.

Including the registry in the baseimage is is good idea, because we then explicitly instead of implicitly use Docker Hub. Buildah / Podman might use other registries instead otherwise.

Pinning the workflow dependencies as been done, as requested by DevOps / generally a good idea.

References

Fixes VTA-589

Checklist

• Tests