Implement deep research

Implements deep research for agentic reasoning.

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From v0.17.0 onward, RAGFlow supports integrating agentic reasoning in an AI chat. The following diagram illustrates the workflow of RAGFlow's deep research:

To activate this feature:

1. Enable the Reasoning toggle in Chat setting.

2. Enter the correct Tavily API key to leverage Tavily-based web search:

The following is a screenshot of a conversation that integrates Deep Research: