Build `Docker Distribution Pruner` with Omnibus to aid with Registry cleanup
As part of the issue https://gitlab.com/gitlab-org/gitlab-ce/issues/25322 and process of streamlining support for Docker Distribution Pruner and making this useful this issue aims to introduce pruner into GitLab Omnibus.
Work needed to be done:
- Build an application with Omnibus,
- Provide comprehensive documentation of how to (today) enable scheduled cleanup.
This is to help with https://gitlab.com/gitlab-org/gitlab-ce/issues/25322, the steps of streamlining the project are described in docker-distribution-pruner#20 (closed).