Fix Text2SQL (#2131)

### What problem does this PR solve?

Fix exeSQL component 
Update DB Assistant template 
Fix canvas Message window size

### Type of change

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

---------

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

agent/canvas.py

@@ -260,7 +260,7 @@ class Canvas(ABC):
 
     def get_history(self, window_size):
         convs = []
-        for role, obj in self.history[window_size * -2:]:
+        for role, obj in self.history[(window_size + 1) * -1:]:
             convs.append({"role": role, "content": (obj if role == "user" else
                                                     '\n'.join(pd.DataFrame(obj)['content']))})
         return convs