Support iframe chatbot. (#3961)

### What problem does this PR solve?

#3909

### Type of change

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

agent/canvas.py

@@ -330,4 +330,7 @@ class Canvas(ABC):
                 q["value"] = v
 
     def get_preset_param(self):
-        return self.components["begin"]["obj"]._param.query
+        return self.components["begin"]["obj"]._param.query
+
+    def get_component_input_elements(self, cpnnm):
+        return self.components["begin"]["obj"].get_input_elements()