GKE provider tutorial - insructions for creating GKE

[darkn3rd]

What happened: Instructions to create GKE are invalid. (ref)

What you expected to happen: The instructions would be valid, instead:

ERROR: (gcloud.container.clusters.create) One of [--zone, --region] must be supplied: Please specify location.

How to reproduce it (as minimally and precisely as possible):

gcloud container clusters create "external-dns" \
    --num-nodes 1 \
    --scopes "https://www.googleapis.com/auth/ndev.clouddns.readwrite"

Anything else we need to know?: Using the default compute GSA is dangerous as this can be used for privilege escalation. This is on top of using a scope to grant all GKE nodes to access Cloud DNS zones.

Environment:

• External-DNS version (use external-dns --version): v0.11.0
• DNS provider: CloudDNS
• Kubernetes: 1.21.10-gke.2000

[darkn3rd]

This can be assigned to me (@darkn3rd), I am working on a PR.