Asyncio issue with flask when run with eventlet or greenlet

[sattvikc]

Steps to reproduce:

• Create a supertokens app using python flask framework.
• run the generated backend using gunicorn + eventlet gunicorn app:app -k eventlet --timeout 1000 -w 1 --bind 0.0.0.0:3001
• Update Call API to make multiple requests in parallel

Some of the requests will fail with 500 error stating Event loop is already running

We might need to implement a separate middleware for flask to support asyncio.