public ServerBuilder startStopExecutor(Executor startStopExecutor) {
        this.startStopExecutor = requireNonNull(startStopExecutor, "startStopExecutor");
        return this;
    }
Sets the {@link Executor} which will invoke the callbacks of {@link Server#start()},
{@link Server#stop()} and {@link ServerListener}.
core/src/main/java/com/linecorp/armeria/server/ServerBuilder.java