Publish GET modules using the Terraform module Registry

Currently we have two options for consuming modules from GET:

1. Vendor the entire project
2. Use symlinks or submodules for referencing the gitlab-environment-toolkit/terraform/modules directory

Ideally we would publish all GET modules and consume them from our own Terraform, perhaps https://docs.gitlab.com/ee/user/packages/terraform_module_registry/ would make this easy? Similar to https://gitlab.com/gitlab-org/quality/gitlab-environment-toolkit/-/merge_requests/224 for Ansible, having a way to consume individual modules will reduce the complexity of projects that are doing their best to avoid DRY by using existing Terraform that GET has for reference architectures.