Fix: document and sdk support of searching message with user_id (#14283)

### What problem does this PR solve?

Add document of search message with user_id, add sdk support.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update

docs/references/python_api_reference.md

@@ -2589,7 +2589,8 @@ Ragflow.search_message(
     query: str, 
     memory_id: list[str], 
     agent_id: str=None, 
-    session_id: str=None, 
+    session_id: str=None,
+    user_id: str=None,
     similarity_threshold: float=0.2, 
     keywords_similarity_weight: float=0.7, 
     top_n: int=10
@@ -2616,6 +2617,10 @@ The ID of the message's source agent. Defaults to `None`.
 
 The ID of the message's session. Defaults to `None`.
 
+##### user_id: `string`, *Optional*
+
+The user participating in the conversation with the agent. Defaults to `None`.
+
 ##### similarity_threshold: `float`, *Optional*
 
 The minimum cosine similarity score required for a message to be considered a match. A higher value yields more precise but fewer results. Defaults to `0.2`.