[UNOFFICIAL] Doc release for v1.13.0 library release

[mmacy]

Important

This PR is for the UNOFFICIAL documentation for the OpenAI Python library at https://mmacy.github.io/openai-python/.

In this PR:

• Integrates changes from upstream release: 1.13.0 openai/openai-python#1148
• Fixes Document the difference between resources.completions and resources.chat.completions #4
• Adds class and init docstrings for OpenAI (sync client only; AsyncOpenAI still to come but need to figure out include strategy)
• Adds a module (or package) docstring for openai
• Adds module docstrings for several modules, including:
  • beta
  • beta.assistants
  • beta.threads
  • chat
  • chat.completions
  • completions
  • embeddings
  • files
  • fine_tuning
  • fine_tuning.jobs
  • images
  • models
  • moderations

Other stuff:

• Added Add doc versioning to support vNext #6 in response to wanting to stage these docs for library v1.13.0 prior to its release
• Added [bug] mkdocstrings-python not publishing docstrings for function overloads #7 as an issue to investigate