Mirror used NPM packages into GitLab

With 11.7, GitLab is launching NPM repository support.

While we don't have full binary proxy support yet to transparently cache upstream resources, we could build a small script to mirror the NPM packages we use at GitLab into a repository.

This would allow us to dogfood our own features, as well as reduce some bandwidth consumption by caching it locally.

I think the main hurdle here is that we currently require all NPM packages uploaded to gitlab to be scoped, rather than the flat list, because of name conflict issues across groups/projects.