This container can be pulled via:
  docker pull registry.opensuse.org/home/mwilck/containers/sle15-sp4/containers/build-kernel:0.1
  docker pull registry.opensuse.org/home/mwilck/containers/sle15-sp4/containers/build-kernel:0.1.6.1

Set DOCKER_CONTENT_TRUST=1 to enable image tag verification.