sysupdate: Add separate polkit actions for cancellation (#42209)

This allows us to have a separate, more permissive, policy for
cancelling ongoing sysupdate jobs. The new default policy for
cancellation actions is to allow them for the active user, without admin
authentication, because typically the user can just pull the plug on the
computer to cancel a job anyway.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>
Fixes: https://github.com/systemd/systemd/issues/38568