make cites in conversation API configurable (#576)

### What problem does this PR solve?

#566

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/db/services/dialog_service.py

@@ -136,7 +136,7 @@ def chat(dialog, messages, **kwargs):
     chat_logger.info("User: {}|Assistant: {}".format(
         msg[-1]["content"], answer))
 
-    if knowledges and prompt_config.get("quote", True):
+    if knowledges and (prompt_config.get("quote", True) and kwargs.get("quote", True)):
         answer, idx = retrievaler.insert_citations(answer,
                                                    [ck["content_ltks"]
                                                        for ck in kbinfos["chunks"]],

docs/conversation_api.md

@@ -221,6 +221,7 @@ This will be called to get the answer to users' questions.
 |------|-------|----|----|
 | conversation_id| string | No | This is from calling /new_conversation.|
 | messages| json | No | All the conversation history stored here including the latest user's question.|
+| quote | bool | Yes | Default: true |
 
 ### Response 
 ```json