Allow Users to view the retrieved excerpts in ChatQnA

[yogeshmpandey]

Currently, in the ChatQnA Demo application, users cannot view the excerpts retrieved from the knowledge base and used by the Language Model (LLM) to generate the answers. It would be beneficial for users to see these excerpts, as it would provide transparency into the reasoning process of the LLM and help users understand the context and sources of the generated answers.