multiarch support

• https://www.docker.com/blog/multi-arch-images/
• https://docs.docker.com/build/building/multi-platform/
• https://www.cloud-computing-koeln.de/multi-arch-build-what-about-travis/

Known Issues on GitLab Registry:

• https://gitlab.com/gitlab-org/gitlab/-/issues/232815 (https://gitlab.com/gitlab-org/gitlab/-/issues/341939)