[Bug] AutoClusterFailover method probeAvailable() always return true if the brokers are behind loadbalancer

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Version

OS: Linux
Pulsar client version: 2.11.1
Pulsar broker version: 2.9.3

### Minimal reproduce step

1/ Deploy two pulsar broker clusters with geo-replication enabled on Kubernetes (AKS) with Istio
2/ Configure Istio virtual service to expose pulsar-proxy service (load balancer)
3/ A consumer utilizes auto-failover pulsar client to consume messages from pulsar brokers
4/ While the consumer is consuming from the primary broker, scale down pulsar-proxy service on the primary broker

### What did you expect to see?

The consumer should consume from secondary broker

### What did you see instead?

The consumer did not switch to the secondary broker as the probeAvailable() method returns true because the load balancer is still up

### Anything else?

I think it would be better if we change to call pulsar admin API for probeAvailable() method instead of socket.connect()

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start by locating the AutoClusterFailover client code and its probeAvailable() method, then trace how socket.connect() determines broker availability behind the load balancer. Reproduce the primary proxy scale-down scenario and verify that the consumer switches to the secondary broker without treating the still-up load balancer as broker availability.

Written by the indexing model from the issue text.