Document the client parameter for endpoint functions

[johnthagen]

Describe the bug

New docstring work in #551 added nicer docstrings, but fails to document the client parameter.

This leads PyCharm to put up Missing parameter in docstring warning for all of these parameters.

To Reproduce

Open generated code in PyCharm 2021.3

Configure:

• Settings | Search "Docstrings"

  • Tools | Python Integrated Tools | Docstrings | Docstring Format: Google

This would probably also flag on darglint, but I have not tested.

Expected behavior

If some args are documented, document all of them to avoid IDEs and linters from throwing warnings.

Desktop (please complete the following information):

• OS: macOS 10.15.7
• Python Version: 3.9.8
• openapi-python-client version: 0.10.8