Fix O(n²) performance in get_message_list by replacing insert(0) with append+reverse (#21588)

Co-authored-by: Jordan <CenteredAxis@users.noreply.github.com>

backend/open_webui/utils/misc.py

@@ -93,12 +93,11 @@ def get_message_list(messages_map, message_id):
     message_list = []
 
     while current_message:
-        message_list.insert(
-            0, current_message
-        )  # Insert the message at the beginning of the list
+        message_list.append(current_message)
         parent_id = current_message.get("parentId")  # Use .get() for safety
         current_message = messages_map.get(parent_id) if parent_id else None
 
+    message_list.reverse()
     return message_list