Feat: Allow operators inside the loop operator to reference the output parameters of external operators #3221 (#8498)

### What problem does this PR solve?

Feat: Allow operators inside the loop operator to reference the output
parameters of external operators #3221

### Type of change


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

web/src/pages/agent/constant.tsx

@@ -646,7 +646,16 @@ export const initialEmailValues = {
 export const initialIterationValues = {
   items_ref: '',
 };
-export const initialIterationStartValues = {};
+export const initialIterationStartValues = {
+  outputs: {
+    item: {
+      type: 'unkown',
+    },
+    index: {
+      type: 'integer',
+    },
+  },
+};
 
 export const initialCodeValues = {
   lang: 'python',