Goal

• As a RHEL Image Mode user, I want to use the familiar DNF interface to test packages on bootc systems without rebuilding and rebooting.

Acceptance criteria

• User can make changes to the system with dnf4 --transient that reset on reboot
• Running with --transient throws an error on non-bootc systems
• Running with or without --transient works when /usr is already writable (e.g. bootc usr-overlay was run manually)
• Users should be able to make transient mode the default in dnf.conf, e.g. by setting persistence=transient.
• It should be very clear to bootc users that changes are not going to persist across reboots like they would on regular mutable systems.