[js-repo-migration] Give Cradle tests a singular home in this repo

With #134, the `.feature` Cucumber files which lived in `apollo-server` will now live in this repository. The copies that existed in `apollo-server` had previously been acting as the single source of truth, but we were _copying_ them (manually) over to this repository in order to verify the conformance of the new Rust query planner.

That means there are now two copies in this repository! We should move them into a (likely, top-level) folder and give them a README on how to use them and remove the duplicated copies in a way that allows the places they are depended on (within this repo) to rely on the single source of truth.