Feat: Redesign and refactor agent module (#9113)

### What problem does this PR solve?

#9082 #6365

<u> **WARNING: it's not compatible with the older version of `Agent`
module, which means that `Agent` from older versions can not work
anymore.**</u>

### Type of change

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

agent/component/iteration.py

@@ -24,10 +24,18 @@ class IterationParam(ComponentParamBase):
 
     def __init__(self):
         super().__init__()
-        self.delimiter = ","
+        self.items_ref = ""
+
+    def get_input_form(self) -> dict[str, dict]:
+        return {
+            "items": {
+                "type": "json",
+                "name": "Items"
+            }
+        }
 
     def check(self):
-        self.check_empty(self.delimiter, "Delimiter")
+        return True
 
 
 class Iteration(ComponentBase, ABC):
@@ -38,8 +46,13 @@ class Iteration(ComponentBase, ABC):
             if self._canvas.get_component(cid)["obj"].component_name.lower() != "iterationitem":
                 continue
             if self._canvas.get_component(cid)["parent_id"] == self._id:
-                return self._canvas.get_component(cid)
+                return cid
+
+    def _invoke(self, **kwargs):
+        arr = self._canvas.get_variable_value(self._param.items_ref)
+        if not isinstance(arr, list):
+            self.set_output("_ERROR", self._param.items_ref + " must be an array, but its type is "+str(type(arr)))
+
+
 
-    def _run(self, history, **kwargs):
-        return self.output(allow_partial=False)[1]