Correct documentation and use of type hints

We should upgrade graphene to use modern type hints. In that process, type hints should be removed from the class/method documentation to have the code as the single source of truth for typing.
We can use https://github.com/tox-dev/sphinx-autodoc-typehints to automatically add type hints back into the docs.

PRs addressing this issue should at least fix the entire file they are contributing to reduce double-checking effort and streamline the process.

Known issues:
#1100 , see #1282 (`Query` on schema)