Auto-generate example project per service

Generates a basic cabal configuration and Makefile plumbing per service, located under `amazonka-*/examples`.

This makes it simpler to drop in some basic service example code into `src/Examples.hs` and quickly test things, with the added benefit of advertising the use of the service in question.

It also keeps step with the related service version, and the `amazonka` and `amazonka-core` libraries.

Everything is relatively pathed to the top-level sandbox.