static RetryRule onStatusClass(HttpStatusClass statusClass) {
        return onStatusClass(statusClass, Backoff.ofDefault());
    }
Returns a newly created {@link RetryRule} that will retry with
the {@linkplain Backoff#ofDefault() default backoff} if the class of the response status is
the specified {@link HttpStatusClass}.
core/src/main/java/com/linecorp/armeria/client/retry/RetryRule.java