Consider using metadata-action for Docker image tags

[mikegerber]

https://github.com/docker/metadata-action

This would enable having:

• semver tags
• having a latest tag that points to the latest semver'ed image
• having a branch tag (e.g. "master" for the latest master)

[mikegerber]

👀 @joschrew

This probably needs some discussion w.r.t. what's wanted for OCR-D.

[mikegerber]

(note that this also solves the "latest should not be master but the latest stable" "problem")

[bertsky]

Good points, but I don't think we should create a dependency on this specific action. Our Docker builds are diversified (CircleCI vs Github Actions, Makefile, labels in Dockerfile) and usually separate build and push. Even just here in ocrd_calamari it would entail lots of changes to use that action.

But providing tags with proper release version and branch in addition to latest would be good. (Also we should add the OCI labels in addition to the old label schema everywhere.)

Recommend moving to spec. (@kba could do it.)