Fix parameter name error. (#4312)

### What problem does this PR solve?

### Type of change

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

api/db/services/canvas_service.py

         conv = {
             "id": session_id,
             "dialog_id": cvs.id,
-            "user_id": kwargs.get("usr_id", "") if isinstance(kwargs, dict) else "",
+            "user_id": kwargs.get("user_id", "") if isinstance(kwargs, dict) else "",
             "message": [{"role": "assistant", "content": canvas.get_prologue()}],
             "source": "agent",
             "dsl": cvs.dsl