refactor: RAG Refactor (#985)

Co-authored-by: Aralhi <xiaoping0501@gmail.com>
Co-authored-by: csunny <cfqsunny@163.com>

examples/rag/rewrite_rag_example.py

@@ -0,0 +1,42 @@
+import asyncio
+import os
+
+from dbgpt.model import OpenAILLMClient
+from dbgpt.rag.retriever.rewrite import QueryRewrite
+
+"""Query rewrite example.
+    pre-requirements:
+        1. install openai python sdk
+        ```
+            pip install openai
+        ```
+        2. set openai key and base
+        ```
+            export OPENAI_API_KEY={your_openai_key}
+            export OPENAI_API_BASE={your_openai_base}
+        ```
+        or 
+        ```
+            import os
+            os.environ["OPENAI_API_KEY"] = {your_openai_key}
+            os.environ["OPENAI_API_BASE"] = {your_openai_base}
+        ```
+    Examples:
+        ..code-block:: shell
+            python examples/rag/rewrite_rag_example.py
+"""
+
+
+async def main():
+    query = "compare steve curry and lebron james"
+    llm_client = OpenAILLMClient()
+    reinforce = QueryRewrite(
+        llm_client=llm_client,
+        model_name="gpt-3.5-turbo",
+    )
+    return await reinforce.rewrite(origin_query=query, nums=1)
+
+
+if __name__ == "__main__":
+    output = asyncio.run(main())
+    print(f"output: \n\n{output}")