Add CI configuration for Kubernetes

Add CI configuration for Kubernetes

Configure Gitlab CI to run on Kubernetes
according to the official documentation.
https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#docker-in-docker-with-tls-enabled-in-kubernetes

These changes are needed because of the CI jobs
using Docker-in-Docker (dind).
As soon as Docker-in-Docker is replaced with Kaniko,
these changes can be reverted.

I documented what I did to set up the Kubernetes runner on the wiki:
https://wiki.qemu.org/Testing/CI/KubernetesRunners

Signed-off-by: Camilla Conte <cconte@redhat.com>
Message-Id: <20230407145252.32955-1-cconte@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>