Use buildah for building images
This MR changes the build system to use buildah
instead of the old docker-in-docker
setup for creating the CI images. This has the massive advantage of not having to expose root access on the CI host system to the CI jobs. All jobs instead run as a normal, unprivileged user on the host.
This requires a CI runner which uses a podman-based custom executor.
Edited by Steffen Müthing