Create a /users/token/refresh endpoint

[chouinar]

Summary

Create a new endpoint that refreshes a token.

This endpoint should use the new api_jwt_auth from #2959

The only thing this endpoint needs to do is a simple update on the expires_at timestamp in the user token session. This should use the same/similar logic to how we set the expires_at in the api_jwt_auth.py code.

You can fetch the current user token session by doing api_jwt_auth.current_user

NOTE: It will seem a bit odd, but you must do db_session.add(user_token_session) in the endpoint in order to actually modify it. This has to do with some complex under-the-hood details on how the DB sessions work (in short - the DB session the API uses and that auth uses is different so we need to make the API one aware of it).

Request
There is no request body for this endpoint, the auth token itself is handled by connecting auth to the endpoint

Response
The response is also very simple, we just want a very basic Response Schema without a relevant data object - see what the Healthcheck endpoint does. We really just want to return a message like Token refreshed when successful.

Note on testing
For unit tests, you can make a valid token by doing something like:

    user = UserFactory.create()
    token, _ = create_jwt_for_user(user, db_session)
    db_session.commit()  # need to commit here to push the session to the DB

    # then freely use the token to call the endpoint

Acceptance criteria

• Endpoint created
• Token expires_at updated and validated in tests
• Basic tests (endpoint gives auth errors if token already expired / isn't valid - which is implemented in the auth logic itself)