Add ability to disable creation of dns zone for unmanaged installs

Similar to managed installs, add ability to optionally create
DNS zones for unmanged installs.

Author: sadasu

api/v1beta1/types_class.go

@@ -459,6 +459,10 @@ type NetworkClassSpec struct {
 	// +optional
 	PrivateDNSZoneName string `json:"privateDNSZoneName,omitempty"`
 
+	// PrivateDNSZone enables private dns zone creation modes for private cluster.
+	// +optional
+	PrivateDNSZone *string `json:"privateDNSZone,omitempty"`
+
 	// PrivateDNSZoneResourceGroup defines the resource group to be used for Azure Private DNS Zone.
 	// If not specified, the resource group of the cluster will be used to create the Azure Private DNS Zone.
 	// +optional

api/v1beta1/zz_generated.deepcopy.go

@@ -559,7 +559,7 @@ func (s *ClusterScope) VNetSpec() azure.ASOResourceSpecGetter[*asonetworkv1api20
 
 // PrivateDNSSpec returns the private dns zone spec.
 func (s *ClusterScope) PrivateDNSSpec() (zoneSpec azure.ResourceSpecGetter, linkSpec, recordSpec []azure.ResourceSpecGetter) {
-	if s.IsAPIServerPrivate() {
+	if s.IsAPIServerPrivate() && s.AzureCluster.Spec.NetworkSpec.PrivateDNSZone != ptr.To(infrav1.PrivateDNSZoneModeNone) {
 		resourceGroup := s.ResourceGroup()
 		if s.AzureCluster.Spec.NetworkSpec.PrivateDNSZoneResourceGroup != "" {
 			resourceGroup = s.AzureCluster.Spec.NetworkSpec.PrivateDNSZoneResourceGroup