Use npmjs as the default registry on Web UI JX pipeline

We are currently relying on https://packages.nuxeo.com/repository/npm-all/ as our default registry on the Web UI JX pipeline. However, it consistently suffers from caching issues, resulting on a lot of broken builds. The goal would be to point to https://registry.npmjs.org and only use https://packages.nuxeo.com/repository/npm-public/ for @nuxeo scoped packages.