Investigate labels creation to GitHub workflows

[sbesson]

Container annotations following the OCI image specification are currently defined in the Dockerfile

omero-server-docker/Dockerfile

Lines 3 to 5 in 3a39707

	LABEL org.opencontainers.image.created="unknown"
	LABEL org.opencontainers.image.revision="unknown"
	LABEL org.opencontainers.image.source="https://github.com/openmicroscopy/omero-server-docker"

Their value is updated as part of the release workflow in

omero-server-docker/Makefile

Lines 36 to 38 in 3a39707

	perl -i -pe 's/OMERO_VERSION=(\S+)/OMERO_VERSION=$(VERSION)/' Dockerfile
	perl -i -pe 's/(org.opencontainers.image.created=)"([^"]+)"/$$1"$(RELEASE)"/' Dockerfile
	perl -i -pe 's/(org.opencontainers.image.revision=)"([^"]+)"/$$1"$(COMMIT)"/' Dockerfile

It might be worth investigating the labels field of docker/build-push-action maybe re-using the workflow defined in https://github.com/docker/build-push-action/blob/646552f0a10fc45d23fb5d14bdae567ea53969e3/docs/advanced/tags-labels.md for creating these labels as part of the GitHub workflow.

An advantage of this approach is that combined with the removal of the build/push action, it might make the wrapping Makefile redundant with a single git tag -s x.y.z-b && git push required for triggering the release of a new set of images.