Webservice: List issued certificates

This does not resolve Call list of certificates for a user via API #419 as that specifies getting certificates for a user, not from a date.
Added filter userid and customcertid

Author: michallohnisky

classes/external.php

@@ -271,6 +271,8 @@ public static function list_issues($timecreatedfrom = null, $userid = null, $cus
 
         $params = [
             'timecreatedfrom' => $timecreatedfrom,
+            'userid' => $userid,
+            'customcertid' => $customcertid,
         ];
         self::validate_parameters(self::list_issues_parameters(), $params);