Some months ago, Stream team decided to start building gen2 image (imagebuilder) but through different tags

The current koji-gc policy is cleaning up old images but only for c*s-guest-candidate tags and not the gen2 ones

We got Zabbix monitoring warning about netapp/nfs thresholds being met (so cleaning up artifacts would be needed)

So koji-gc policy should be adapted to start untagging old images, that will land in trashcan tag and then be removed