Make `frontend`, `static_landing` and `backend` stacks all depend on `url_registry` stack

[dsiguero]

Currently:
backend -> url_registry -> [frontend, static_landing]

Future:
url_registry -> [backend, frontend, static_landing]

(array [] notation indicates they're all in the same group)

Wait at least until the QA environment is deployed to ensure we don't run into API GW DNS propagation issues when running automated tests.