Add docs on how to manage proxied SSL for other GitLab components
Add docs on how to manage proxied SSL for other GitLab components

GitLab supports proxied SSL on many different components. The
current documentation was not clear on this. Now it's specifically
called out and an example is given (Registry).

gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab