feat(llm): support basic rag api(v1)

[ChenZiHong-Gavin]

There may be 2 ways to integrate fastapi into the gradio app:

1. use python client provided by Gradio
2. encapsulate asynchronous HTTP call process

refer:

1. https://www.gradio.app/guides/sharing-your-app
2. https://www.gradio.app/guides/fastapi-app-with-the-gradio-client