[Usecase] RepoSync

We use an Ubuntu LTS with Docker to have repository proxy using [Sonatype Nexus3](https://hub.docker.com/r/sonatype/nexus3/)

For some distro (RHEL) we want to keep every installable package other times even if not anymore online.

We can do a reposync but :
1/ I don't want to consume both time some space
2/ I want everything in the same interface (Nexus3)

Nexus3 don't manage mirrors, so I create a docker redhat-ubi using my Nexus proxy to do a reposync.

It will place all file in my proxy and don't use space twice cause reposync use a nullfs ;-)

To do that you need nullfs loaded on the host (Ubuntu) and docker --privileged for container can use mount

Thx again for your amazing work