CDNs don't cache responses with Set-Cookie header as they assume they
contain some sort of state or user-specific data, which is not the case for
raw blobs and repository archives.

This change allows GitLab installations that sit behind a CDN to benefit from its
caching feature seamlessly.

Related to https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/6829
and https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/4