Include sscg by default alongside cockpit
    
    Cockpit 140+ will now use sscg if it is available to generate more
    reliable and secure default certificates instead of simple
    self-signed certificates.
    
    Fedora Server carries only a reduced set of Cockpit subpackages,
    so it doesn't pick up the `Recommends: sscg` from the main
    'cockpit' metapackage. Thus we need to add it explicitly in the
    comps.xml
    
    Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>