fix(性能测试): 修复批量添加监控项有问题的缺陷

--bug=1025344 --user=王孝刚 [性能测试] github
#235781.20.21-lts版本，性能测试批量添加监控项有问题。
https://www.tapd.cn/55049933/s/1362022

performance-test/frontend/src/business/test/components/EditMonitor.vue

@@ -58,6 +58,7 @@
 
 import MsDialogFooter from "metersphere-frontend/src/components/MsDialogFooter";
 import MonitorKeyValue from "./MonitorKeyValue";
+import {KeyValue} from "metersphere-frontend/src/model/ScenarioModel";
 
 export default {
   name: "EditMonitor",
@@ -92,6 +93,9 @@ export default {
         }
         this.form = copy;
       }
+      if (this.monitorList.length === 0) {
+          this.monitorList.push(new KeyValue({enable: true}));
+      }
       if (index !== '' && index !== undefined) {
         this.index = index;
       }
@@ -99,6 +103,7 @@ export default {
     closeFunc() {
       this.form = {};
       this.dialogVisible = false;
+      this.monitorList = [];
     },
     update() {
       this.$refs.monitorForm.validate(valid => {