Add Multibjets/MBJ_Analysis tagged images (21.2.*) from gitlab registry

As described in #4 (closed), I've added the service account cvmfsunpacker as a reporter to the project. Presumably, this is all that's needed in order to get access, so let's see?

recipe.yaml

@@ -59,3 +59,4 @@ input:
     - 'https://registry.hub.docker.com/atlasamglab/stats:latest'
     - 'https://registry.hub.docker.com/atlasamglab/stats:root6.20.00'
     - 'https://registry.hub.docker.com/fnallpc/fnallpc-docker:*'
+    - 'https://gitlab-registry.cern.ch/gitlab-registry.cern.ch/multibjets/mbj_analysis:21-2*'