static <T extends Response> RetryRuleWithContent<T> onServerErrorStatus(Backoff backoff) {
        return RetryRuleWithContent.<T>builder().onServerErrorStatus().thenBackoff(backoff);
    }
Returns a newly created {@link RetryRuleWithContent} that will retry with the specified {@link Backoff}
if the class of the response status is {@link HttpStatusClass#SERVER_ERROR}.
core/src/main/java/com/linecorp/armeria/client/retry/RetryRuleWithContent.java