### 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"] 
```



x-pack/plugin/shutdown/qa/multi-node/src/javaRestTest/java/org/elasticsearch/xpack/shutdown/NodeShutdownIT.java
"target node name parameter is only valid for REPLACE-type shutdowns",
                            type,
                            equalToIgnoringCase("replace")
                        );
                        putBody.field("target_node_name", targetNodeName);
                    }
                }
                putBody.endObject();
                putShutdown.setJsonEntity(Strings.toString(putBody));
            }
        }
        assertOK(client().performRequest(putShutdown));
    }
    @SuppressWarnings("unchecked")
    private String getRandomNodeId() throws IOException {
        Request nodesRequest = new Request("GET", "_nodes");
        Map<String, Object> nodesResponse = responseAsMap(client().performRequest(nodesRequest));
        Map<String, Object> nodesObject = (Map<String, Object>) nodesResponse.get("nodes");
        return randomFrom(nodesObject.keySet());
    }
    @Override
    protected Settings restClientSettings() {
        String token = basicAuthHeaderValue(
            System.getProperty("tests.rest.cluster.username"),
            new SecureString(System.getProperty("tests.rest.cluster.password").toCharArray())
        );
        return Settings.builder().put(ThreadContext.PREFIX + ".Authorization", token).build();
    }
}