/chat-messages Endpoint streaming model add message_start event, response retriever_resources

[yuhaowin]

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1. Is this request related to a challenge you're experiencing?

I used dify build a RAG application，and sometimes LLM will have hallucinations,especially when no retriever_resources is found, so if not retriever_resources I'll reponse the constant sentence.

2. Describe the feature you'd like to see

If I can get this information at the first time,I can immediately discard the content generated by LLM.

3. How will this feature improve your workflow or experience?

RAG applications will have more credibility.

4. Additional context or comments

No response

5. Can you help us with this feature?

• [ ] I am interested in contributing to this feature.