Add support for jh/jest.config.js

jest.config.js

+const fs = require('fs');
+const IS_JH = require('./config/helpers/is_jh_env');
 const baseConfig = require('./jest.config.base');
 
-module.exports = {
-  ...baseConfig('spec/frontend'),
-};
+// TODO: Remove existsSync once jh has added jest.config.js
+if (IS_JH && fs.existsSync('./jh/jest.config.js')) {
+  // eslint-disable-next-line global-require, import/no-unresolved
+  module.exports = require('./jh/jest.config');
+} else {
+  module.exports = {
+    ...baseConfig('spec/frontend'),
+  };
+}