[victoria-metrics-k8s-stack] Use global.cluster.dnsDomain in all URL generation

[dctrwatson]

Since the default ndots config is 5 for pods, it would reduce load on kube-dns if all k8s service hostnames had the cluster's dnsDomain appended to them.

EG: vmalertmanager-vm-stack-0.vmalertmanager-vm-stack.monitoring.svc.cluster.local.

While I don't think most VM components resolve DNS often, it's nice not to have them performing 6 or more DNS queries when they do.