Add mutation planning tests to cradle suite (#4390)

Ported some tests from the existing mutation integration tests (from the gateway).
I commented which those were and their corresponding tests from the gateway package (since I changed some names slightly)
so we could go back later when we port _all_ tests to cucumber and remove them from this one mega-file :)

I also added a simple, barebones, single-service test to make sure mutations build a simple fetch node to begin with