Docker register on branches
Changes the .gitlab-ci.yml in order to publish the docker images on the registry with tag name inferred from branch names.
pattern: ci-transient-$CI_COMMIT_BRANCH
This prepares for https://gitlab.inria.fr/stemcovid19/tac-server/backend-server/-/issues/23
it also simplifies the main .gitlab-ci.yml
by using an external script in .gitlab-ci
folder