Provide a requests session to Uploader [Feature Request]

[peterroelants]

It would make the library more flexible if the Uploader could be given a requests Session object which it uses to make all requests.

Custom requests sessions can be used for many things. For example, I use them myself to capture all 401 Unauthorized errors when my tokens are expired, make sure I'm re-authenticated and repeat the request. I've seen others use them to fix a URL base or adding custom headers.

Would tus-py-client maintainers be open to providing the ability to initialize an Uploader with a custom requests.Session object to enable use cases like this?