static GracefulShutdownSupport create(Duration quietPeriod, Executor blockingTaskExecutor) {
        return create(quietPeriod, blockingTaskExecutor, Ticker.systemTicker());
    }
Keeps track of pending requests to allow shutdown to happen after a fixed quiet period passes
after the last pending request.
core/src/main/java/com/linecorp/armeria/server/GracefulShutdownSupport.java