Added GitLab CI for proxy images.

2 jobs for master in 1 minute and 8 seconds (queued for 4 seconds)
Name Stage Failure
failed
20-04-weekly Proxy Image
WARNING! Your password will be stored unencrypted in /root/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store

Login Succeeded
$ LOCAL_IMAGE_URL=$CI_REGISTRY_IMAGE:$DOCKER_TAG
$ docker pull $DOCKER_IMAGE:$DOCKER_TAG
Error response from daemon: manifest for docker:20.04 not found
ERROR: Job failed: exit code 1