Verify kubernetes-nmstate works in disconnected environments

Many baremetal deployments are done disconnected, and as a result we need to ensure it is possible to install and use the operator in such an environment. This is also needed for some dev scenarios such as ipv6 or ipv4 with image mirroring enabled.

This will involve mirroring the kubernetes-nmstate images to the local registry. I know there is existing documentation for this process and will add a link here when I find it.