Add support for GKE Autopilot

This is supported in the Terraform provider: https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/container_cluster#enable_autopilot

Official documentation: https://cloud.google.com/kubernetes-engine/docs/concepts/autopilot-overview

Autopilot is a new mode of operation in Google Kubernetes Engine (GKE) that is designed to reduce the operational cost of managing clusters, optimize your clusters for production, and yield higher workload availability.

The key bit is:

Pay per Pod resource requests (CPU, memory, and ephemeral storage) instead of Pay per node (CPU, memory, boot disk)