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/http_api_reference.md

@@ -6629,6 +6629,10 @@ curl --location 'http://{address}/api/v1/messages/search?query=%22who%20are%20yo
 
   The ID of the message's session. Defaults to `None`.
 
+- `user_id`: (*Filter parameter*), `string`, *Optional*
+
+  The user participating in the conversation with the agent. Defaults to `None`.
+
 - `similarity_threshold`: (*Filter parameter*), `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`.

docs/references/python_api_reference.md

@@ -2590,6 +2590,7 @@ Ragflow.search_message(
     memory_id: list[str], 
     agent_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`.

sdk/python/ragflow_sdk/ragflow.py

@@ -341,12 +341,13 @@ class RAGFlow:
             raise Exception(res["message"])
         return res["message"]
 
-    def search_message(self, query: str, memory_id: list[str], agent_id: str=None, session_id: str=None, similarity_threshold: float=0.2, keywords_similarity_weight: float=0.7, top_n: int=10) -> list[dict]:
+    def search_message(self, query: str, memory_id: list[str], agent_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) -> list[dict]:
         params = {
             "query": query,
             "memory_id": memory_id,
             "agent_id": agent_id,
             "session_id": session_id,
+            "user_id": user_id,
             "similarity_threshold": similarity_threshold,
             "keywords_similarity_weight": keywords_similarity_weight,
             "top_n": top_n