Add `py.typed` to Python client library

[DanielNoord]

The code is typed, but due to lack of a py.typed in the source (and final distribution) type checkers will not know this.

Would be good to add this file, ensure it is packaged and add the Trove classifier to indicate on PyPI that this package is typed.

[luis-eduardo-code]

Hello,
I'm interested in contributing. How can I help?

[DanielNoord]

This issue is pretty hard to pick up if you don't have previous experience with adding py.typed to a distribution. I would recommend looking for a different issue/repository to look into :)