Private docker registry

[namnguyen5497]

Hi, Im currently using airgapped environment for cnf_testsuites. I'm looking for a way to config a private docker registry for cluster-tools, dockerd, etc...
I found some old issues and pull requests but they're from version 0.2x, like this one https://github.com/cncf/cnf-testsuite/pull/624/files?diff=split&w=0.
The current version's documents also not mentioning about using private docker registry
Is there a way to configure this ?

Thanks