OCPBUGS-29068: GCP: Skip validation of public and private zones for terraform vars

** During the GCP installation with custom dns configuration enabled, the
private and public zones should not be validated (skip them), so that there are
not errors when they cannot be found.

Author: barbacbd

pkg/asset/cluster/tfvars/tfvars.go

@@ -490,23 +490,27 @@ func (t *TerraformVariables) Generate(parents asset.Parents) error {
 		preexistingnetwork := installConfig.Config.GCP.Network != ""
 
 		// Search the project for a dns zone with the specified base domain.
+		// When the user has selected a custom DNS solution, the zones should be skipped.
 		publicZoneName := ""
-		if installConfig.Config.Publish == types.ExternalPublishingStrategy {
-			publicZone, err := client.GetDNSZone(ctx, installConfig.Config.GCP.ProjectID, installConfig.Config.BaseDomain, true)
-			if err != nil {
-				return errors.Wrapf(err, "failed to get GCP public zone")
-			}
-			publicZoneName = publicZone.Name
-		}
-
 		privateZoneName := ""
-		if installConfig.Config.GCP.NetworkProjectID != "" {
-			privateZone, err := client.GetDNSZone(ctx, installConfig.Config.GCP.ProjectID, installConfig.Config.ClusterDomain(), false)
-			if err != nil {
-				return errors.Wrapf(err, "failed to get GCP private zone")
+
+		if installConfig.Config.GCP.UserProvisionedDNS != gcp.UserProvisionedDNSEnabled {
+			if installConfig.Config.Publish == types.ExternalPublishingStrategy {
+				publicZone, err := client.GetDNSZone(ctx, installConfig.Config.GCP.ProjectID, installConfig.Config.BaseDomain, true)
+				if err != nil {
+					return errors.Wrapf(err, "failed to get GCP public zone")
+				}
+				publicZoneName = publicZone.Name
 			}
-			if privateZone != nil {
-				privateZoneName = privateZone.Name
+
+			if installConfig.Config.GCP.NetworkProjectID != "" {
+				privateZone, err := client.GetDNSZone(ctx, installConfig.Config.GCP.ProjectID, installConfig.Config.ClusterDomain(), false)
+				if err != nil {
+					return errors.Wrapf(err, "failed to get GCP private zone")
+				}
+				if privateZone != nil {
+					privateZoneName = privateZone.Name
+				}
 			}
 		}