Move relayer main package and related configs to it's own subfolder

[iansuvak]

Context and scope
After #368 is merged we should do some clean up and move relayer specific main, api and config packages and to the relayer subfolder.

TODOs before merging

• Reorganize configs such that we can explicitly confirm that relayer config and signature aggregator config both implement peers.Config interfaces.
• Extract duplicative e2e test functionality for running a binary into a helper function that both applications use.
• Re-evaluate locations of scripts, build and testing
• Re-evaluate passing configs around by reference

Discussion and alternatives

Open questions

• Should we consider renaming the repo at this point? To what?