Allow polkadot-parachain logic to be reused

[gilescope]

(for example integration tests currently duplicate genesis information because it can't pull this info in as a dep)

[gilescope]

There's a lot of logic in that crate that others may wish to make use of rather than having to replicate. It's rarely helpful to have a lot of logic in a rust binary, best to hand off to a library asap because at some point someone wants to reuse that logic.