### Description

The new [readiness port](https://www.elastic.co/guide/en/elasticsearch/reference/8.4/advanced-configuration.html#readiness-tcp-port) makes readiness checks on Kubernetes much easier. However the current implementation only allows connections through localhost. TCP probes on Kubernetes are run by the kubelet which is a process running on the Kubernetes node (and not from within the container or the Pod). The [Kubernetes documentation](https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/#tcp-probes) mentions it, but it is kind of subtle: 

> For a TCP probe, the kubelet makes the probe connection at the node, not in the pod, which means that you can not use a service name in the host parameter since the kubelet is unable to resolve it.


That means a standard Kubernetes readiness probe cannot be used for Elasticsearch:
```
          readinessProbe:
            tcpSocket:
              port: 8080
```

Instead, only an `exec` probe that runs a shell command inside the container can be used that relies in this case on the presence of the `nc` command in the container image:

```
    readinessProbe:
      exec:
        command: ["nc", "-z", "-v", "-w5", "127.0.0.1", "8080"] 
```



server/src/main/java/org/elasticsearch/readiness/ReadinessService.java
return;
        }
        this.serverChannel = setupSocket();
        this.listenerThreadLatch = new CountDownLatch(1);
        new Thread(() -> {
            assert serverChannel != null;
            try {
                while (serverChannel.isOpen()) {
                    AccessController.doPrivileged((PrivilegedAction<Void>) () -> {
                        try (SocketChannel channel = serverChannel.accept()) {} catch (IOException e) {
                            logger.debug("encountered exception while responding to readiness check request", e);
                        } catch (Exception other) {
                            logger.warn("encountered unknown exception while responding to readiness check request", other);
                        }
                        return null;
                    });
                }
            } finally {
                listenerThreadLatch.countDown();
            }
        }, "elasticsearch[readiness-service]").start();
        logger.info("readiness service up and running on {}", boundAddress().publishAddress());
    }
    @Override
    protected void doStop() {
        this.active = false;
        stopListener();
    }
    
    synchronized void stopListener() {