Customer commented in RHDHBUGS-203 that it would be great to clarify in the docs what the `app.baseUrl`, `backend.baseUrl` and `backend.cors.origin` fields should point to exactly, especially when running RHDH behind a reverse proxy.
These URLs should be what the user sees in their browser when accessing RHDH.

• the properties app.baseURL, backend.baseURL and backend.cors.origin must point to the external URL of the reverse proxy, e.g. my.public.domain.
• the developer hub must be exposed under the root path, which means no context path on the reverse proxy
• the oidc property metadataUrl must be pointing to an url on the reverse proxy (e.g. sso.public.domain, for the clients), but must also be reachable from the developer hub backend (we had some issues here, because openshift had no connectivity to the reverse proxy).

More context in RHDHBUGS-203