horizontal_pod_autoscaling should be enabled by default

You have `horizontal_pod_autoscaling` disabled by default. In Terraform (https://www.terraform.io/docs/providers/google/r/container_cluster.html) it's **enabled** by default though. Why have the opposite? It seems to me that generic Terraform modules should not change the default behavior of the original resources they are wrappers for, unless there's a good reason.