Password authentication

mixtral generated this actually very usable description:

This pull request adds a function get_token to the chatai library, which allows users to obtain a token for authentication using their username and password. This is useful for users who do not want to manually extract their token from their browser cookies.

Additionally, the interactive_chat.py example has been updated to use the new get_token function, and the README.md has been updated with instructions on how to use this function to authenticate.