This PR begins to address #104 by:

• Removing defaults in variables.tf where user input is required
• Use a terraform.default.tfvars to guide users on required variables
• Removes local-exec in Cloud DNS configuration, replacing with a direct Terraform resource

This also fixes #105 by using direct role references rather than interpolated strings, fixing a bug where Terraform would try to apply a permission before the custom role was created.

Note: The build is still failing on a few issues, but this should be a good baseline update that will help make it easier to isolate those with future PRs.