Environment-based configuration of DeriveClient

[forkedcancel]

An attempt at partially(?) resolving #9.

I used shocon to handle dev and prod application.conf files on the scalajs side. I'm not sure this is the best way of making both ./deploy.sh and zio-app dev send requests to their respective intended backends, but it works, and lets me push a client and server that reside on different (sub)domains.

There are no changes to the backend route generation - being able to push the frontend to firebase and the backend to heroku/dokku was all I was trying to accomplish, hence 'partially.'

[kitlangton]

Wow! That's amazing 😄 Thanks so much for doing this.

I think there's some first-class CORS support for zio-http, but I can muck with that in a follow-up commit. I think I'd prefer some means of code-config over HOCON files—however, this works and fits with a framework paradigm. I may investigate that further in some later PRs, but this gets the job done and makes a lot of sense. Once again, thanks so much!