Add llm op

Signed-off-by: Kaiyuan Hu <kaiyuan.hu@zilliz.com>

eqa_search.py

@@ -108,6 +108,7 @@ def enhanced_qa_search_pipe(config):
     p = (
         p.map('result', 'docs', lambda x:[i[2] for i in x])
             .map(('question', 'docs', 'history'), 'prompt', ops.prompt.question_answer())
+            .map('prompt', 'answer', ops.LLM.OpenAI(api_key=config.openai_api_key))
     )
 
-    return p.output('question', 'history', 'docs', 'prompt')
+    return p.output('answer')