Audit GCP hosts for unmanaged IPtables rules

Corrective action from https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/8528

18. Audit where there are (or will be) unmanaged iptables rules on hosts that have or currently do use the gitlab-iptables chef cookbook.

After https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/8638 is complete, we should audit remaining prod hosts for unmanaged rules and make follow up issues for anything we find.