Add JS to enable ES EE functionality

- Update changelog

ee/app/assets/javascripts/pages/admin/application_settings/index.js

@@ -2,6 +2,77 @@ import '~/pages/admin/application_settings/index';
 
 import groupsSelect from '~/groups_select';
 
+import 'select2/select2';
+import $ from 'jquery';
+import { s__ } from '~/locale';
+import Api from '~/api';
+
+const onLimitCheckboxChange = (checked, $limitByNamespaces, $limitByProjects) => {
+  $limitByNamespaces.find('.select2').select2('data', null);
+  $limitByNamespaces.find('.select2').select2('data', null);
+  $limitByNamespaces.toggleClass('hidden', !checked);
+  $limitByProjects.toggleClass('hidden', !checked);
+};
+
+const getDropdownConfig = (placeholder, apiPath, textProp) => ({
+  placeholder,
+  multiple: true,
+  initSelection($el, callback) {
+    callback($el.data('selected'));
+  },
+  ajax: {
+    url: Api.buildUrl(apiPath),
+    dataType: 'JSON',
+    quietMillis: 250,
+    data(search) {
+      return {
+        search,
+      };
+    },
+    results(data) {
+      return {
+        results: data.map(entity => ({
+          id: entity.id,
+          text: entity[textProp],
+        })),
+      };
+    },
+  },
+});
+
 document.addEventListener('DOMContentLoaded', () => {
   groupsSelect();
+
+  // ElasticSearch
+  const $container = $('#js-elasticsearch-settings');
+
+  $container
+    .find('.js-limit-checkbox')
+    .on('change', e =>
+      onLimitCheckboxChange(
+        e.currentTarget.checked,
+        $container.find('.js-limit-namespaces'),
+        $container.find('.js-limit-projects'),
+      ),
+    );
+
+  $container
+    .find('.js-elasticsearch-namespaces')
+    .select2(
+      getDropdownConfig(
+        s__('Elastic|None. Select namespaces to index.'),
+        Api.namespacesPath,
+        'full_path',
+      ),
+    );
+
+  $container
+    .find('.js-elasticsearch-projects')
+    .select2(
+      getDropdownConfig(
+        s__('Elastic|None. Select projects to index.'),
+        Api.projectsPath,
+        'name_with_namespace',
+      ),
+    );
 });