GitLab.com CI artifacts to use Google Cloud CDN

What this post added

This post details the migration of GitLab CI artifact downloads from Google Cloud Storage to Google Cloud CDN. This change aims to improve download speeds for CI users by leveraging edge caches. The implementation involves redirecting artifact download requests to `cdn.artifacts.gitlab-static.net` instead of `storage.googleapis.com`, with exceptions for requests originating from within Google Cloud Platform. The post also outlines potential impacts on users with firewalls and provides guidance on troubleshooting common error messages.