@UnstableApi
    public ServerBuilder gracefulShutdown(GracefulShutdown gracefulShutdown) {
        this.gracefulShutdown = requireNonNull(gracefulShutdown, "gracefulShutdown");
        return this;
    }
Sets the {@link GracefulShutdown} configuration.
If not set, {@link GracefulShutdown#disabled()} is used.
core/src/main/java/com/linecorp/armeria/server/ServerBuilder.java