GKE tutorial falsely claims it's possible to create LE certificate without domain (only IP)

[vasekhodina]

In section 4 of the GKE deployment tutorial there is a note saying that if you cannot buy a domain, you can continue without it and use IP address instead of domain. Rest of the tutorial uses Let's Encrypt. However as mentioned in https://github.com/cert-manager/cert-manager/issues/6863 it is not possible to create a certificate for an IP with Let's encrypt. The note should be deleted.