static RetryRule onStatusClass(Iterable<HttpStatusClass> statusClasses, Backoff backoff) {
        return builder().onStatusClass(statusClasses).thenBackoff(backoff);
    }
Returns a newly created {@link RetryRule} that will retry with the specified {@link Backoff} if the
class of the response status is one of the specified {@link HttpStatusClass}es.
core/src/main/java/com/linecorp/armeria/client/retry/RetryRule.java