[Bug] Disaggregated cluster backends register internal addresses despite LoadBalancer service type

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/doris-operator/issues?q=is%3Aissue) and found no similar issues.

### Version

- **Doris Operator Version**: 25.7.0 (or your current version)
- **Doris Version**: 3.1 (disaggregated mode)
- **Cloud Provider**: AWS EKS (or your provider)

### What's Wrong?

When deploying a disaggregated Doris cluster with compute groups configured to use `LoadBalancer` service type, the backends register with their internal Kubernetes addresses (Pod FQDN or internal IP) instead of the external LoadBalancer addresses. This makes the backends inaccessible from outside the Kubernetes cluster.

### What You Expected?

When `show backends` is executed, it should show external LoadBalancer addresses that are accessible from outside the cluster when the service type is `LoadBalancer`.

### How to Reproduce?

_No response_

### Anything Else?

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

No source file, test, or entry point is named. Start by reproducing a disaggregated Doris 3.1 cluster on AWS EKS with a LoadBalancer compute-group service, then inspect show backends and compare the registered addresses with the external service addresses; done means external LoadBalancer addresses are shown.

Written by the indexing model from the issue text.