The current public_dns zone in the GCP provider doesn't work

[nacx]

When deploying the management plane in GCP, there is a bit of flexibility when configuring the FQDN. Users can create a FQDN with the .private suffix to create an internal zone, and can use any other name that is not the gcp.cx.tetrate.info and a public DNS zone will be created.

However, that zone needs to be explicitly configured so that other projects (and clusters can see it), and this is something that needs to be done beforehand, by pointing the Domain to the nameservers in that zone. This breaks the CP deployment in GCP if using this approach.

In order to fix it, public zones should be assumed to exist (like we do with the shared one) instead of being created, and the project in which they exist should be configurable.
This is a small change I already fixed in my fork (last 3 files of this commit): nacx@bf8b200