Automation tab in VM creation page should mention that it relies on qemu-guest-agent being installed in the guest system

[travier]

While trying to understand how https://github.com/cockpit-project/cockpit-machines/pull/1150 is effectively implemented, I've realized that this relies on https://wiki.qemu.org/Features/GuestAgent and https://wiki.libvirt.org/Qemu_guest_agent.html and thus needs the qemu-guest-agent to be installed and running in the Guest system.

One notable system that does not include the QGA is Fedora CoreOS (see https://github.com/coreos/fedora-coreos-tracker/issues/74).

The suggestion is thus to include a notice somewhere on this tab that this relies on the agent to be there in the guest.