Omnibus Docker image for GitLab does not have docker registry working by default

When trying to setup GitLab using the omnibus docker image, the docker registry in GitLab is not active by default.

Following the directions on https://docs.gitlab.com/omnibus/docker/, there is no docker registry (5000) port exposed. Further, after launching GitLab from the docker image, in the admin panel, the registry is not turned on. According to the docs (https://docs.gitlab.com/ee/administration/packages/container_registry.html), as of 12.5, the registry should be turned on by default.

The documentation for using the Omnibus Docker image should be updated to reflect access to the registry. Additionally, it appears that some bug exists that prevents the registry from being turned on by default.