Rename terraform modules packages.rb file to namespace_packages.rb

Context

In New API class for terraform modules project end... (!137824 - merged), we introduced a new project-level API class, and the purpose of this class was to include all project-level endpoints in the Terraform Registry. Thus, we moved all project-level endpoints from the existing API::Terraform::Modules::V1::Packages class to the new API::Terraform::Modules::V1::ProjectPackages class.

Now all endpoints in the API::Terraform::Modules::V1::Packages class are namespace-level ones. Therefore, this class should be renamed to API::Terraform::Modules::V1::NamespacePackages to reflect its purpose accurately and to be consistent with the naming convention we have for the class that contains the project-level endpoints and the one that contained the namespace-level ones.