Take a look at quay.io/foreman/foreman:3.1-stable (quay.io/foreman/foreman). That image is maintained by the project and comes from a Docker Compose setup for development (see https://github.com/theforeman/foreman/).
I have a running Docker Customize setup for productive use that leverages that image at https://github.com/painless-software/synology-foreman. Not all plugins are successfully configured yet, but maybe it can help as a source of inspiration.