Move integration specs module name mappers

This MR moves the module-name-mappers, which are specific to
the integration suit from jest.config.base to jest.config.integration.

jest.config.base.js

 const IS_EE = require('./config/helpers/is_ee_env');
 const isESLint = require('./config/helpers/is_eslint');
 
-module.exports = (path) => {
+module.exports = (path, options = {}) => {
+  const {
+    moduleNameMapper: extModuleNameMapper = {},
+    moduleNameMapperEE: extModuleNameMapperEE = {},
+  } = options;
+
   const reporters = ['default'];
 
   // To have consistent date time parsing both in local and CI environments we set
@@ -45,8 +50,7 @@ module.exports = (path) => {
     'emojis(/.*).json': '<rootDir>/fixtures/emojis$1.json',
     '^spec/test_constants$': '<rootDir>/spec/frontend/__helpers__/test_constants',
     '^jest/(.*)$': '<rootDir>/spec/frontend/$1',
-    '^test_helpers(/.*)$': '<rootDir>/spec/frontend_integration/test_helpers$1',
-    '^ee_else_ce_test_helpers(/.*)$': '<rootDir>/spec/frontend_integration/test_helpers$1',
+    ...extModuleNameMapper,
   };
 
   const collectCoverageFrom = ['<rootDir>/app/assets/javascripts/**/*.{js,vue}'];
@@ -57,9 +61,9 @@ module.exports = (path) => {
       '^ee(/.*)$': rootDirEE,
       '^ee_component(/.*)$': rootDirEE,
       '^ee_else_ce(/.*)$': rootDirEE,
-      '^ee_else_ce_test_helpers(/.*)$': '<rootDir>/ee/spec/frontend_integration/test_helpers$1',
       '^ee_jest/(.*)$': '<rootDir>/ee/spec/frontend/$1',
       [TEST_FIXTURES_PATTERN]: '<rootDir>/tmp/tests/frontend/fixtures-ee$1',
+      ...extModuleNameMapperEE,
     });
 
     collectCoverageFrom.push(rootDirEE.replace('$1', '/**/*.{js,vue}'));

jest.config.integration.js

 const baseConfig = require('./jest.config.base');
 
 module.exports = {
-  ...baseConfig('spec/frontend_integration'),
+  ...baseConfig('spec/frontend_integration', {
+    moduleNameMapper: {
+      '^test_helpers(/.*)$': '<rootDir>/spec/frontend_integration/test_helpers$1',
+      '^ee_else_ce_test_helpers(/.*)$': '<rootDir>/spec/frontend_integration/test_helpers$1',
+    },
+    moduleNameMapperEE: {
+      '^ee_else_ce_test_helpers(/.*)$': '<rootDir>/ee/spec/frontend_integration/test_helpers$1',
+    },
+  }),
 };