feat: loop start add index (#3101)

* feat: loop start add index

* update doc

packages/web/i18n/en/workflow.json

@@ -1,5 +1,6 @@
 {
   "Array_element": "Array element",
+  "Array_element_index": "Index",
   "Code": "Code",
   "Confirm_sync_node": "It will be updated to the latest node configuration and fields that do not exist in the template will be deleted (including all custom fields).\n\nIf the fields are complex, it is recommended that you copy a node first and then update the original node to facilitate parameter copying.",
   "Node.Open_Node_Course": "Open node course",

packages/web/i18n/zh/workflow.json

@@ -1,5 +1,6 @@
 {
   "Array_element": "数组元素",
+  "Array_element_index": "下标",
   "Code": "代码",
   "Confirm_sync_node": "将会更新至最新的节点配置，不存在模板中的字段将会被删除（包括所有自定义字段）。\n如果字段较为复杂，建议您先复制一份节点，再更新原来的节点，便于参数复制。",
   "Node.Open_Node_Course": "查看节点教程",