public ServerListenerBuilder whenStopped(Consumer<? super Server> consumer) {
        serverStoppedCallbacks.add(requireNonNull(consumer, "consumer"));
        return this;
    }
Add a {@link Consumer} invoked when the {@link Server} is stopped.

@see ServerListener#serverStopped(Server)
core/src/main/java/com/linecorp/armeria/server/ServerListenerBuilder.java