Merge constants into a single file

ee/app/assets/javascripts/subscriptions/constants.js

 import { s__ } from '~/locale';
 
+export const ZUORA_SCRIPT_URL = 'https://static.zuora.com/Resources/libs/hosted/1.3.1/zuora-min.js';
+
+export const PAYMENT_FORM_ID = 'paid_signup_flow';
+
+export const ZUORA_IFRAME_OVERRIDE_PARAMS = {
+  style: 'inline',
+  submitEnabled: 'true',
+  retainValues: 'true',
+};
+
 export const ERROR_FETCHING_COUNTRIES = s__('Checkout|Failed to load countries. Please try again.');
 export const ERROR_FETCHING_STATES = s__('Checkout|Failed to load states. Please try again.');
+export const ERROR_LOADING_PAYMENT_FORM = s__(
+  'Checkout|Failed to load the payment form. Please try again.',
+);
 
 // The order of the steps in this array determines the flow of the application
 /* eslint-disable @gitlab/require-i18n-strings */

ee/app/assets/javascripts/subscriptions/new/components/checkout/zuora.vue

 <script>
 import { GlLoadingIcon } from '@gitlab/ui';
 import { mapState, mapActions } from 'vuex';
-import { ZUORA_SCRIPT_URL, ZUORA_IFRAME_OVERRIDE_PARAMS } from 'ee/subscriptions/new/constants';
+import { ZUORA_SCRIPT_URL, ZUORA_IFRAME_OVERRIDE_PARAMS } from 'ee/subscriptions/constants';
 
 export default {
   components: {

ee/app/assets/javascripts/subscriptions/new/constants.js

-export const ZUORA_SCRIPT_URL = 'https://static.zuora.com/Resources/libs/hosted/1.3.1/zuora-min.js';
-
-export const PAYMENT_FORM_ID = 'paid_signup_flow';
-
-export const ZUORA_IFRAME_OVERRIDE_PARAMS = {
-  style: 'inline',
-  submitEnabled: 'true',
-  retainValues: 'true',
-};
-
 export const TAX_RATE = 0;
 
 export const NEW_GROUP = 'new_group';

ee/app/assets/javascripts/subscriptions/new/store/actions.js

 import Api from 'ee/api';
+import { PAYMENT_FORM_ID } from 'ee/subscriptions/constants';
 import { GENERAL_ERROR_MESSAGE } from 'ee/vue_shared/purchase_flow/constants';
 import activateNextStepMutation from 'ee/vue_shared/purchase_flow/graphql/mutations/activate_next_step.mutation.graphql';
 import createFlash from '~/flash';
 import { redirectTo } from '~/lib/utils/url_utility';
 import { sprintf, s__ } from '~/locale';
-import { PAYMENT_FORM_ID } from '../constants';
 import defaultClient from '../graphql';
 import * as types from './mutation_types';