docs: Fix service name in port-forward command (#5527)

Signed-off-by: Orange Ng <ngquanhao@outlook.com>
Co-authored-by: Neal Vaidya <nealv@nvidia.com>

docs/kubernetes/installation_guide.md

@@ -281,7 +281,7 @@ kubectl get pods -n ${NAMESPACE}
    kubectl apply -f examples/backends/vllm/deploy/agg.yaml -n ${NAMESPACE}
 
    # Port forward and test
-   kubectl port-forward svc/agg-vllm-frontend 8000:8000 -n ${NAMESPACE}
+   kubectl port-forward svc/vllm-agg-frontend 8000:8000 -n ${NAMESPACE}
    curl http://localhost:8000/v1/models
    ```