OCPBUGS-38689: Add section for xpn deletion permissions

** The docs leave out the permissions for deleting firewalls in a gcp xpn install. The
section is added to include the 3 permissions to do so.

Author: barbacbd

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

@@ -25,6 +25,13 @@ Ensure that the host project applies one of the following configurations to the
 * `roles/compute.securityAdmin`
 ====
 
+.Required permissions for deleting firewalls in the host project
+[%collapsible]
+====
+* `compute.firewalls.delete`
+* `compute.networks.updatePolicy`
+====
+
 .Required minimal permissions
 [%collapsible]
 ====