Add external zones in nodelocaldns configuration (#5591)

Allows to configure additionnal zone for domains not resolved by `upstream_dns_servers`.

inventory/sample/group_vars/k8s-cluster/k8s-cluster.yml

@@ -139,6 +139,19 @@ dns_mode: coredns
 enable_nodelocaldns: true
 nodelocaldns_ip: 169.254.25.10
 nodelocaldns_health_port: 9254
+# nodelocaldns_external_zones:
+# - zones:
+#   - example.com
+#   - example.io:1053
+#   nameservers:
+#   - 1.1.1.1
+#   - 2.2.2.2
+#   cache: 5
+# - zones:
+#   - https://mycompany.local:4453
+#   nameservers:
+#   - 192.168.0.53
+#   cache: 0
 # Enable k8s_external plugin for CoreDNS
 enable_coredns_k8s_external: false
 coredns_k8s_external_zone: k8s_external.local