Mark externally managed terraform resources to make infrastructure terraform appliable throughout its lifetime (#442)

* Mark externally managed terraform resources to make infrastructure terraform appliable throughout its lifetime
* Use correct field for nat gateway

Signed-off-by: Paul Meyer <49727155+katexochen@users.noreply.github.com>
Co-authored-by: Paul Meyer <49727155+katexochen@users.noreply.github.com>

cli/internal/terraform/terraform/gcp/modules/instance_group/main.tf

@@ -94,4 +94,11 @@ resource "google_compute_instance_group_manager" "instance_group_manager" {
       port = named_port.value.port
     }
   }
+
+  lifecycle {
+    ignore_changes = [
+      target_size, # required. autoscaling modifies the instance count externally
+      version,     # required. update procedure modifies the instance template externally
+    ]
+  }
 }