Migrate resource gitlab_project_tag from terraform SDK to Framework plugin

Migrate the gitlab_project_tag resource (defined in internal/provider/sdk/resource_gitlab_project_tag.go) from the old SDK to the new terraform Framework plugin.

Functionality for the Read/Create/Update/Delete functions should be the same as the old SDK resource. The new version should be created under the internal/provider folder. Tests should be equal between the two resources. There should be a new test checking that users can migrate from the old to the new version without errors. The old version should be deleted.

Run the make reviewable command before raising a merge request.