use templatefile function with template files

[codeangler]

https://github.com/PaloAltoNetworks/google-cloud-vmseries-ncc-tutorial/blob/51439d12a699ebb480c0433a7ec53dcfed951e43/region1.tf#L97-L106

this may be preferable ... https://developer.hashicorp.com/terraform/language/functions/templatefile instead of "file()"

Because our deployment pipelines don't have a persistent state, the file is written each time, and the plan says that the file will change. Maybe this software won't be impacted, but using the templatefile function could help with Terraform internals.