hashicorp/template provider is deprecated

Hi, 

Thanks for a great repo to get started with Consul on GCP!

This repository is using `template_file` from the provider `hashicorp/template`, which is deprecated.
https://github.com/hashicorp/terraform-provider-template/issues/85

```data "template_file" "startup_script_client"``` should be replaced by the function `templatefile`.

BR
Fredrik