Rely on packages.nuxeo.com when building Web UI images

We are currently relying on our JX team npm proxy and group repos (http://nexus/repository/npmjs-all/) when building Web UI. We should instead rely on
https://packages.nuxeo.com/repository/npm-all/ to avoid potential Nexus cache issues, at least until we change our publishing strategy to drop the republishing of snapshot versions which lead to integrity check errors due to different checksum between blob and metadata.