Support Clusterapi-k3s for GCP

[thusharajayakody1]

while trying to use the bootstrap and controlplane provider with GCP. seems like it is not supported and GCP falls back to kubeadm provider

• request to add support for the gcp infrastructure
• add documentation in samples for better clarity if already supported

will be happy to test a RC if any is present

[nasusoba]

I have not seen samples with GCP. Also, the current sample is kind of outdated. I have tested the latest in Azure and this would work Azure ClusterClass template. Maybe you could try modify based on mine.

We indeed needs to update the samples :(