Pass OIDC access token from go server to Python client

We are already passing the username and subject ID to python client. The access token of a user is needed as well to be able for python SDK to authenticate user in e.g. MLops.

## Goal
Make the current OIDC access token available from python client. Make it accessible from `q.auth.access_token`.

Part of https://github.com/h2oai/h2o-ai-cloud/issues/139