Add stage 4 waiting room

[Carifio24]

This PR adds an implementation of the stage 4 waiting room. The behavior here differs slightly from the Voila version in that we now activate the advance button when enough students have completed their data, rather than the abrupt transition in the Voila version.

At the moment this si a bit difficult to test. I was able to test the class data polling functionality by continually using a dynamic checking condition:

    async def keep_checking_class_data():
        count = 0
        enough_students_ready = Ref(LOCAL_STATE.fields.enough_students_ready)
        while not enough_students_ready.value:
            points = load_class_data()
            count += 1
            ready = len(points) >= 100 - 10 * count
            # Some logging statements for checking values
            logger.info(100 - 10 * count)
            logger.info(ready)
            logger.info(enough_students_ready.value)
            logger.info("======")
            if ready:
                enough_students_ready.set(True)
            await asyncio.sleep(2)  # This sets how often (in seconds) we re-check the class data

Also, if you then want to reset the enough_students_ready in your student's story state, you can run

UPDATE cosmicds_db.StoryStates 
SET story_state = JSON_SET(story_state, '$.story.enough_students_ready', false)
WHERE student_id = <your-student-id>;

[Carifio24]

Marking as a draft again while I make some updates to handle some items from #660.