Add URI system records for KDC
    
    MIT KRB5 1.15 introduced KDC service discovery with URI records.
    _kerberos and _kpasswd URI records can provide TCP, UDP, and Kerberos
    KDC-Proxy references. URI lookups take precedence over SRV lookups,
    falling back to SRV lookups if no URI records are found.
    
    Also reduce TTL for system records from one day to one hour. It allows
    users to remove or update discovery entries in a timely fashion.
    
    See: https://web.mit.edu/kerberos/krb5-latest/doc/admin/realm_config.html#kdc-discovery
    Fixes: https://pagure.io/freeipa/issue/8968
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>