Add identifier to oauth profile

This is needed for nextcloud

data/web/oauth/profile.php

@@ -14,6 +14,7 @@ if (!empty($mailbox)) {
     echo json_encode(array(
       'success' => true,
       'username' => $token['user_id'],
+      'identifier' => $token['user_id'],
       'email' => (!empty($mailbox['username']) ? $mailbox['username'] : ''),
       'full_name' => (!empty($mailbox['name']) ? $mailbox['name'] : 'mailcow administrative user'),
       'created' => (!empty($mailbox['created']) ? $mailbox['created'] : ''),