Add a docker proxy registry on packages for ARender

We want to add a new docker repository in order to proxy the ARondor docker repository: https://artifactory.arondor.cloud:5001.

We currently have docker-arender.packages.nuxeo.com where we store images we built for ARender integration.

Ideally, we would like to be able to pull our images and ARondor ones from the same docker repository on packages. This means we need to add a docker proxy repository to ARondor and a docker group repository grouping the current hosted repository and this proxy.

We won't need to access the docker proxy directly, usage will always go through the group. But we need to access the docker hosted one in order to push images we need to.