Automatically delete stale Docker images created by the triggered build
Related to https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2234
When build is triggered from CE, eg. https://gitlab.com/gitlab-org/gitlab-ce/builds/15661103, we create and push a Docker image to registry: https://gitlab.com/gitlab-org/omnibus-gitlab/container_registry .
We should have an automatic cleanup setup to cleanup images that are older than X days.