chore: add getters:{} to cli-plugin-vuex template (#6753)

Author: puxiao

packages/@vue/cli-plugin-vuex/generator/template-vue3/src/store/index.js

@@ -3,6 +3,8 @@ import { createStore } from 'vuex'
 export default createStore({
   state: {
   },
+  getters: {
+  },
   mutations: {
   },
   actions: {

packages/@vue/cli-plugin-vuex/generator/template/src/store/index.js

@@ -6,6 +6,8 @@ Vue.use(Vuex)
 export default new Vuex.Store({
   state: {
   },
+  getters: {
+  },
   mutations: {
   },
   actions: {