fix: zones must be computed to allow api feedback (#739)

Author: bahkauv70

stackit/internal/services/ske/cluster/resource.go

@@ -19,6 +19,7 @@ import (
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/booldefault"
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/int64default"
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/int64planmodifier"
+	"github.com/hashicorp/terraform-plugin-framework/resource/schema/listplanmodifier"
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/mapplanmodifier"
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/objectplanmodifier"
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/planmodifier"
@@ -672,7 +673,11 @@ func (r *clusterResource) Schema(_ context.Context, _ resource.SchemaRequest, re
 							"zones": schema.ListAttribute{
 								Description: "Specify a list of domain filters for externalDNS (e.g., `foo.runs.onstackit.cloud`)",
 								Optional:    true,
+								Computed:    true,
 								ElementType: types.StringType,
+								PlanModifiers: []planmodifier.List{
+									listplanmodifier.UseStateForUnknown(),
+								},
 							},
 						},
 					},