tofu config and docs

.tofu/platforms/upc/modules/cluster/main.tf

@@ -47,6 +47,14 @@ resource "upcloud_kubernetes_node_group" "workers" {
   node_count    = var.node_count
   plan          = var.node_plan
   anti_affinity = var.node_count > 1
+
+  dynamic "cloud_native_plan" {
+    for_each = var.storage_size != null ? [1] : []
+    content {
+      storage_size = var.storage_size
+    }
+  }
+
   labels = {
     prefix  = var.prefix
     cluster = var.cluster_name