Add exception class MDTemporarilyUnavailableException

MDErrorReporter.php

@@ -37,6 +37,7 @@ public static function categorizeError(Throwable $exception):MDErrorCategory {
             || $exception instanceof MDMysqliExpectedError
             || $exception instanceof MDcouldNotSetPublic
             || $exception instanceof MDInvalidNodaLink
+            || $exception instanceof MDTemporarilyUnavailableException
         ) {
             return MDErrorCategory::known;
         }