Adds the page for instance lvl security dashboard

- Adds the route
- Adds the template
- Puts the above behind a feature flag

config/routes.rb

@@ -107,6 +107,7 @@ Rails.application.routes.draw do
     draw :instance_statistics
 
     Gitlab.ee do
+      draw :security
       draw :smartcard
       draw :jira_connect
       draw :username

ee/app/assets/javascripts/pages/security/index.js

+import Vue from 'vue';
+import createStore from 'ee/security_dashboard/store';
+import router from 'ee/security_dashboard/store/router';
+import DashboardComponent from 'ee/security_dashboard/components/app.vue';
+
+if (gon.features && gon.features.securityDashboard) {
+  document.addEventListener(
+    'DOMContentLoaded',
+    () =>
+      new Vue({
+        el: '#js-security',
+        store: createStore(),
+        router,
+        components: {
+          DashboardComponent,
+        },
+        render(createElement) {
+          return createElement(DashboardComponent, {
+            props: {},
+          });
+        },
+      }),
+  );
+}

ee/app/controllers/security_controller.rb

+# frozen_string_literal: true
+
+class SecurityController < ApplicationController
+  before_action :authorize_read_security_dashboard!
+  before_action do
+    push_frontend_feature_flag(:security_dashboard)
+  end
+
+  def authorize_read_security_dashboard!
+    render_404 unless Feature.enabled?(:security_dashboard) &&
+      can?(current_user, :read_security_dashboard)
+  end
+end

ee/app/views/security/index.html.haml

+- page_title _('Security Dashboard')
+- @hide_breadcrumbs = true
+
+#js-security

ee/config/routes/security.rb

+# frozen_string_literal: true
+
+get 'security' => 'security#index'