* Update backend.py
change to the model that received from user interactive from the web interface model selection.
* Update index.html
added Llama2 as a provider selection and also include the model selection for Llama2: llama2-70b, llama2-13b, llama2-7b
* Update requirements.txt
add asgiref to enable async for Flask in api.
"RuntimeError: Install Flask with the 'async' extra in order to use async views"