OCPBUGS-45404: GCP Permissions are required for destroy

** The getIamPolicy and setIamPolicy permissions are required for GCP destroy xpn installations
whether the control plane service account is provided or not.

Author: barbacbd

modules/minimum-required-permissions-ipi-gcp-xpn.adoc

@@ -39,7 +39,7 @@ Ensure that the host project applies one of the following configurations to the
 * `roles/compute.networkUser`
 ====
 
-If you do not supply a service account for control plane nodes in the `install-config.yaml` file, please grant the below permissions to the service account in the host project.
+If you do not supply a service account for control plane nodes in the `install-config.yaml` file, please grant the below permissions to the service account in the host project. If you do not supply a service account for compute nodes in the `install-config.yaml` file, please grant the below permissions to the service account in the host project for cluster destruction.
 
 [%collapsible]
 ====