Fix DNS_UNIQUE_ID so it's not required to be set for DNS flavor (#883)

Author: AshleyDumaine

templates/flavors/k3s/dns-loadbalancing/kustomization.yaml

@@ -19,7 +19,7 @@ patches:
         network:
           loadBalancerType: dns
           dnsRootDomain: ${DNS_ROOT_DOMAIN}
-          dnsUniqueIdentifier: ${DNS_UNIQUE_ID}
+          dnsUniqueIdentifier: ${DNS_UNIQUE_ID:-""}
           dnsProvider: ${DNS_PROVIDER:-"linode"}
           dnsSubDomainOverride: ${DNS_SUBDOMAIN_OVERRIDE:-""}
   - target: