Add support to iframe chatbot (#3929)

### What problem does this PR solve?

#3909

### Type of change

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

agent/canvas.py

@@ -21,6 +21,7 @@ from functools import partial
 from agent.component import component_class
 from agent.component.base import ComponentBase
 
+
 class Canvas(ABC):
     """
     dsl = {
@@ -320,3 +321,13 @@ class Canvas(ABC):
 
     def get_prologue(self):
         return self.components["begin"]["obj"]._param.prologue
+
+    def set_global_param(self, **kwargs):
+        for k, v in kwargs.items():
+            for q in self.components["begin"]["obj"]._param.query:
+                if k != q["key"]:
+                    continue
+                q["value"] = v
+
+    def get_preset_param(self):
+        return self.components["begin"]["obj"]._param.query