Periodically clean up containers+images on ops runner
We should consider periodically cleaning up writeable container layers and images using https://gitlab.com/gitlab-org/gitlab-runner-docker-cleanup on our ops docker runner.
An example of how this is provisioned elsewhere in the CI fleet: https://dev.gitlab.org/cookbooks/packer-runner-machines/blob/master/provisioners/create.sh#L160-188.
This applies to all ops envs (us-central, etc).