DEVOPS-5942: version-tag the Nuclio base image (v3.7.0) like the services
Follow-up to !13 (merged). Tags the image with the git tag verbatim (e.g. v3.7.0) instead of the moving py37 + redundant py37-v3.7.0. Variant is encoded by the version (v3.7.x = python:3.7, v3.11.x = python:3.11); a guard fails the build on a tag/Dockerfile-python mismatch. Clusters will pin the exact version via do_image.
After merge I'll re-cut v3.7.0 to republish with the single versioned tag and delete the old py37/py37-v3.7.0 tags across the replicated repos.