renew agent: allow reusing existing certs
    
    Add a switch which makes `dogtag-ipa-ca-renew-agent-submit` reuse the
    existing certificate rather than request a new one from the CA while
    maintaining LDAP replication of the certificate.
    
    Make this available as a new `dogtag-ipa-ca-renew-agent-reuse` certmonger
    CA.
    
    This allows redoing the LDAP replication and reexecuting pre- and post-save
    commands of a tracking request without reissuing the certificate.
    
    https://pagure.io/freeipa/issue/5799
    
    Reviewed-By: David Kupka <dkupka@redhat.com>
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>