Stop supporting CI/CD template backports

Context

Before there was an official way to use CI/CD components on GitLab self-managed we've started to backport the OpenTofu CI/CD component as CI/CD templates in GitLab. They are available here.

This changed and there is now an official way for how to use the GitLab maintained CI/CD components in GitLab self-managed. See the official documentation here and OpenTofu specific documentation here.

With that, I'm wondering if we should deprecate the OpenTofu CI/CD template (backports) now and stop updating them.

The benefit of this is that we don't need to maintain the machinery to create the backports from the template (ugly Makefile hacks) removing code and cognitive load. It also inherently avoids the feature gap between the component and the template.