Update the indentation of the `virtual_machines` map in `terraform/prod/terraform.tfvars` from 4 spaces to 2 spaces to maintain consistency with the surrounding HCL code style. No functional changes were made to the configuration values.
- Remove `*.tfvars` from .gitignore to allow tracking variable files.
- Enforce Terraform version to be greater than or equal to 1.5.0 in prod configuration.