### 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
/**
     * Returns the current bound address for the readiness service.
     * If Elasticsearch was never ready, this method will return null.
     * @return the bound address for the readiness service
     */
    public BoundTransportAddress boundAddress() {
        InetSocketAddress boundAddress = boundSocket.get();
        if (boundAddress == null) {
            return null;
        }
        TransportAddress publishAddress = new TransportAddress(boundAddress);
        return new BoundTransportAddress(new TransportAddress[] { publishAddress }, publishAddress);
    }
    
    InetSocketAddress socketAddress(InetAddress host, int portNumber) {
        
        var socketAddress = boundSocket.get();
        if (socketAddress == null) {
            socketAddress = new InetSocketAddress(host, portNumber);
        }
        return socketAddress;
    }
    
    ServerSocketChannel setupSocket() {
        InetAddress localhost = InetAddress.getLoopbackAddress();
        int portNumber = PORT.get(environment.settings());
        assert portNumber >= 0;
        try {
            serverChannel = ServerSocketChannel.open();
            AccessController.doPrivileged((PrivilegedAction<Void>) () -> {