feat: add multi-platform Docker images

[masci]

Related Issues

• fixes n/a

Proposed Changes:

Build the new Docker images for both amd64 and arm64 architectures

How did you test it?

• Local build
• Images available here https://hub.docker.com/repository/docker/deepset/haystack/tags?page=1&ordering=last_updated&name=massi

Notes for the reviewer

• The target "docker-metadata-action" was removed because a leftover from an old Github action setup

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added tests that demonstrate the correct behavior of the change
• I've used the conventional commit convention for my PR title
• I documented my code
• I ran pre-commit hooks and fixed any issue

[julian-risch]

The changes look good to me! 👍 I very much like the comment "A note about multi-platform builds..." explaining the error message that some users might get in advance. Very forward-thinking! 👍