Common Docker Documentation Location in `gitlab-ce`

Right now we have a very bare bones set of documentation here: https://gitlab.com/gitlab-org/gitlab-ce/tree/master/docker

And a good set of documentation here: https://docs.gitlab.com/omnibus/docker/

We should:

1. Move away from a readme in the /Docker folder of the gitlab-ce repo, to an actual file in a /doc folder.
2. Keep the Omnibus Docker documentation, as that pertains to the current Docker images that are based on it.
3. Add a new common documentation file in gitlab-ce/docs which links to the Omnibus Docker images, but also can eventually link to our cloud native version as well.

Once this is done we should then:

1. Update our /installation page to direct to this new location

Closes #36828 (closed)