update add_video route and change queue method

- change add to queue method from `GET` on `/` to `POST` on `/queue`
- update `/add_video` route to accept single video url

Dockerfile

@@ -23,4 +23,4 @@ EXPOSE "${PORT_NUMBER}"
 RUN pip3 install --no-cache-dir -r requirements.txt
 
 # Run server.py when the container launches
-CMD gunicorn --bind "${LISTEN_ADDRESS}":"${LISTEN_PORT}" run:app
+CMD gunicorn --bind ${LISTEN_ADDRESS}:${LISTEN_PORT} run:app