Runtime Integration tests

[JoshOrndorff]

Recipes is pretty good about having tests that cover pallets, but not that test the entire runtime which includes how pallets are coupled together as well as the constants in their config traits.

moonbeam-foundation/moonbeam#339

[nuke-web3]

Integration tests is what you are after here, right?
Related request: https://stackoverflow.com/questions/66884974/how-do-you-write-a-system-test-for-your-runtime

This is something I think would be super valuable in general to have on the devhub - as patterns and tools to help with this are (AFAIK) lacking for integration test, where unit tests are fairly covered. cc @sacha-l