Support custom Requests Session Instances

[JLLeitschuh]

I was recently working on a project where I was pulling quite a bit of data from GitHub to generate statistics around thousands of pull requests generated.

In this case, I wanted intercept that response and cache it so that, when I inevitably had a bug in my code I could use the PyGitHub API to re-try pulling that exact same data again, but process it differently. I wanted to be able to do this without hitting the rate-limiter a second time.

Thus, I decided to use requests-cache to intercept the response and enable this.

https://requests-cache.readthedocs.io/en/stable/index.html

However, since PyGitHub doesn't expose an API to change the session instance, I had to use the patch solution to patch the Session object. However, this is less than ideal in a multithreaded application.

[EnricoMi]

I guess getting access to the Session instance that is used by the Requester is sufficient, rather then providing an instance as a github.Github constructor argument.

[JLLeitschuh]

Likely. One other thing I'm thinking about too is that the cache requester wouldn't need a delay before each request if the response is cached. But requests that don't hit the cache will still need a delay. I don't know if there's an easy way to make this work with this library and the current structure of PyGithub