Improve Pokémon Service `Makefile` (#1264)

* Improve Pokémon Service `Makefile`

* Code-generate only the Pokémon Service SDK (as opposed to all targets
  in the `codegen-server-test` subproject like we do currently).
* Add `run` target to run the service.
* Add `doc-open` target to generate and open Rustdoc documentation.
* Bring back client generation

Co-authored-by: Matteo Bigoi <1781140+crisidev@users.noreply.github.com>