Allow using system roles at image or container (bootc) build time. This would allow users to install packages, configure services, write config files, add other files that would be used when the image starts up.

The role should work both without any dbus/systemd services running and with dbus/systemd services running.

The role should work for image builder and bootc Containerfile builds.

The system role should be able to detect if it is running in such an environment and act accordingly, similar to how they can now detect if running on an ostree system by looking at /run/ostree-booted.