Migrate helper Docker images to multi-platform
Description
Currently we have a Dockerfile per platform to build helper images. Following up on what was done for the Runner image on !1861 (merged), we should simplify in the same way the way we're building and distributing our helper images.
Proposal
- Start using
buildx
to build the helper images so we exclusively use thealpine
but still tag the images likegitlab/gitlab-runner-helper:$ARCH-$HASH
- This would unblock work for zOS
- This would unblock us from being stuck on an old alpine version
Links to related issues and merge requests / references
Next steps
- (#25869) Start publishing multi-arch images and phase out the old tagging structure. This will take time and we have to update both Runner code and build process to use it.