Validate cluster name when creating a new cluster via GKE integration

Problem to solve

The GKE integration doesn't seem to validate cluster name when creating a new cluster. This may lead to the elusive Something went wrong while creating your cluster on Google Kubernetes Engine Failed to request to CloudPlatform; Invalid request error. For example, a cluster name that starts with a number will fail to create. Only by creating the cluster in GCP we see that this trips a validation.

Proposal

Validate cluster name according to GCP's guidelines:

Name must start with a lowercase letter followed by up to 40 lowercase letters, numbers, or hyphens, and cannot end with a hyphen

Links / references

ZD: https://gitlab.zendesk.com/agent/tickets/96476 (internal)