Firebase Authentication Route

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We will create a new endpoint /api/auth_hello for user authentication within app.py, such that the API can retrieve user tokens from the front end, confirm the validity of each token with Firebase Admin SDK, and send confirmation of the user verification back to the front end. We have submitted a separate issue for the necessary front end modifications to the front end's Github.

Eventually, we will be able to expand on the functionality of this route, constructing other routes /api/syllabus_upload, /api/get_user_courses that rely on this verification.