Use JX internal Nexus as Docker repository in the Napps Team

The idea is to replace the current docker registry with Nexus and put in place a cleanup policy.
In fact, all images generated by preview ( master and Pull requests) are not cleaned.

Currently we're using the Jenkins X provided Docker registry to deploy images:

• jenkins
• builders
• nuxeo-aspera-connector
• nuxeo-salesforce

See the complete list:

curl https://docker-registry.napps.dev.nuxeo.com/v2/_catalog | jq

This is an issue at least because:

• We're relying on an extra service whereas we already have/need a Nexus for the Maven artifacts.
• We quickly run out of disk space since there is no cleanup policy in the registry, see the frequent: