feat: Add an OOTB Chat uI to the Feature Server to support RAG demo

[franciscojavierarceo]

What this PR does / why we need it:

This pull request introduces several enhancements to the Feast feature server, including the addition of a chat UI, WebSocket support, and improvements to the server's API documentation.

1. MANIFEST.in:
   • Added a new line to include static files in the package.
2. sdk/python/feast/feature_server.py:
   • Imported new modules and libraries (asyncio, os, importlib_resources, WebSocket, WebSocketDisconnect, StaticFiles).
   • Added new classes for chat functionality (ChatMessage, ChatRequest).
   • Extended get_app function to document its purpose and endpoints in detail.
   • Introduced new endpoints:
     - /chat: POST endpoint to process chat requests.
     - /chat: GET endpoint to serve the chat UI.
     - /ws/chat: WebSocket endpoint for real-time chat communication.
   • Created a ConnectionManager class to manage WebSocket connections and handle incoming messages.
3. sdk/python/feast/ui_server.py:
   • Added a check to return a 503 status code if the registry is unavailable.
     4.sdk/python/feast/static/chat/index.html:
   • Added a new HTML file to provide a basic chat UI for the Feast feature server.
     - The UI includes an input box for user messages and a container for displaying chat messages.
     - Integrated WebSocket for real-time chat functionality.

Which issue(s) this PR fixes:

N/A

Misc

The chat looks like this and supports streaming output:

[shuchu]

Lgtm

[dmartinol]

What’s the idea behind this change? 🤔 is this a temporary endpoint or are you prototyping a future enhancement?

[franciscojavierarceo]

Temporary endpoint fora future enhancement.

The goal will be to expose a lightweight chat capability so MLEs can see how to create their RAG applications. Not meant for production but meant for fast prototyping. Streamlit would require more packages. 😊