cacert manage: support PKINIT
    
    Allow installing 3rd party CA certificates trusted to issue PKINIT KDC
    and/or client certificates.
    
    https://pagure.io/freeipa/issue/6831
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>