Katello's REX templates that install content should be able to install it transiently for image mode hosts.

This intro task will first involve researching the current state of DNF's transient package support and understanding the difference between it and `bootc usr-overlay`.

Once the mechanism for installing transient packages is understood, our content-installing job templates should be able to detect if the host is an image mode one and apply the packages transiently automatically.

For hosts that don't support dnf --transient, we either need to enable the bootc usr-overlay or throw an error.