PKI Redesign: setup Ember Engine (#16925)

* setup PKI Ember engine

* clean up SecretListHeader and add documentation.

* move secret-list-header to addon folder

* move options-for-backend helper

* fix all for SecretListHeader to work

* use secretListHeaderTab by moving to adodn.

* add overview empty state

* clean up

* remove secret-list-header and secret-list-header-tab changes to move to another pr

* more cleanup

* update syntax with newer guides

* good idea jordan

ui/lib/pki/addon/engine.js

@@ -0,0 +1,29 @@
+import Engine from '@ember/engine';
+
+import loadInitializers from 'ember-load-initializers';
+import Resolver from 'ember-resolver';
+
+import config from './config/environment';
+
+const { modulePrefix } = config;
+
+export default class PkiEngine extends Engine {
+  modulePrefix = modulePrefix;
+  Resolver = Resolver;
+  dependencies = {
+    services: [
+      'auth',
+      'flash-messages',
+      'namespace',
+      'path-help',
+      'router',
+      'store',
+      'version',
+      'wizard',
+      'secret-mount-path',
+    ],
+    externalRoutes: ['secrets'],
+  };
+}
+
+loadInitializers(PkiEngine, modulePrefix);