Feat: new component variable assigner (#11050)

### What problem does this PR solve?
issue:
https://github.com/infiniflow/ragflow/issues/10427
change:
new component variable assigner
### Type of change

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

agent/component/iteration.py

@@ -32,6 +32,7 @@ class IterationParam(ComponentParamBase):
     def __init__(self):
         super().__init__()
         self.items_ref = ""
+        self.veriable={}
 
     def get_input_form(self) -> dict[str, dict]:
         return {