[11.8] Add confidential filter (GitLabPHP#694)

Author: bastienho

src/Api/Issues.php

@@ -41,6 +41,7 @@ class Issues extends AbstractApi
      *     @var int[]  $iids                 return only the issues having the given iid
      *     @var string $order_by             return requests ordered by created_at or updated_at fields (default is created_at)
      *     @var string $sort                 return requests sorted in asc or desc order (default is desc)
+     *     @var bool $confidential           filter confidential or public issues
      *     @var string $search               search issues against their title and description
      * }
      *
@@ -483,6 +484,9 @@ protected function createOptionsResolver(): OptionsResolver
         $resolver->setDefined('sort')
             ->setAllowedValues('sort', ['asc', 'desc'])
         ;
+        $resolver->setDefined('confidential')
+            ->setAllowedValues('confidential', [false, true])
+        ;
         $resolver->setDefined('search');
         $resolver->setDefined('created_after');
         $resolver->setDefined('created_before');