fix(admin): repair email rollback and product taxonomy APIs

Call the existing Email_Rollback::list_pending method instead of the missing
list_recent_changes method that caused /email-rollback/users to fatal. Add
the product taxonomy route expected by ProductEditorDrawer and return
category/tag options for the editor.

inc/classes/admin/class-aksrt-admin-shop-controller.php

@@ -168,6 +168,13 @@ class AKSRT_Admin_Shop_Controller extends AKSRT_Admin_Controller_Base {
             'permission_callback' => [$this, 'check_permission'],
         ]);
 
+        // Product taxonomy options used by the product editor.
+        register_rest_route(self::API_NAMESPACE, '/shop/products/taxonomy', [
+            'methods'             => 'GET',
+            'callback'            => [$this, 'get_product_taxonomy'],
+            'permission_callback' => [$this, 'check_permission'],
+        ]);
+
         // Product list
         register_rest_route(self::API_NAMESPACE, '/shop/products', [
             'methods'             => 'GET',