Previously one had to configure hardcoded urls to link from one client
application to others since keycloak didn't provide a way to get the
actual client URL by providing clientId and realm information.
We now support a new endpoint with the path {realm}/clients/{client_id}/redirect
that responds to GET requests with a 307 (temporary redirect) with the
configured client URL. This allows to refer to any client just by the
realmName and clientId and let Keycloak redirect to the actual client
application.
Add documentation for new redirect endpoint.
