Add option to use client certificates.

[PhilipMay]

We want to secure our Azure OpenAI access with client certificates. To do this we need the option to add one to "requests".

I do not see an option to do this. If waned I can provide a PR.

[PhilipMay]

The request function of the requests package has an option called cert that needs to be set.

See https://requests.readthedocs.io/en/latest/api/#requests.Session.request

[kristapratico]

@PhilipMay you might try passing in your own requests.Session using the openai.requestssession variable and setting the cert. Something like this:

import requests

session = requests.Session()
session.cert = <your cert>
openai.requestssession = session