spec: libvirt-daemon: Add optional dependency on *-client

spec: libvirt-daemon: Add optional dependency on *-client

The libvirt-daemon subpackage contains libvirt-guests.sh script (used by
libvirt-guests service), which requires virsh to actually work. But
since dynamic libraries were separated from libvirt-client to
libvirt-libs more than 6 years ago, libvirt-daemon no longer requires
virsh to be installed. So unless libvirt-client is explicitly installed
(either manually or by installing the libvirt meta package),
libvirt-guests will not work.

Just adding libvirt-client as a dependency of libvirt-daemon would go
against the original idea behind splitting libvirt-client: users may not
want to install or use any client binaries on the host where the daemon
runs (either they just use various language bindings or access the
daemon remotely). To solve this we could possibly turn libvirt-daemon
into an empty package and separate the daemons and libvirt-guests into
subpackages to make sure we support both use cases, but marking
libvirt-client as Recommended for libvirt-daemon does the same job in a
much simpler way.

https://bugzilla.redhat.com/show_bug.cgi?id=2136591

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>