Publish multi-arch helper images
Description
Once #25487 (closed) is implemented, we'll have helper images being built with docker buildx
(with multi-platform support), but still publishing to the same platform-dependent tags. The goal of this issue is to migrate to a new tag structure which doesn't include the platform.
Proposal
- 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.