adk web support FunctionNode, and start node in creation page

adk v2 has FunctionNode and StartNode, but when I run adk web to create a workflow ,it has no feature of FunctionNode ,
I hope it will be right a graph not tree mode in adk v2, thinks
```
def my_function_node(node_input: Any):
return "你好，世界"

# 带有选项的 FunctionNode 包装器
success_node = FunctionNode(
my_function_node,
name="hello",
rerun_on_resume=True,
)
```