dnszone: deprecate option for setting SOA serial
    
    Since IPA 3 [1] SOA serial is managed automatically via autoincrement,
    and the option of disabling this behavior was deprecated in IPA 3.3.3 [2].
    As a result, the option '--serial' during DNS zone addition would be
    ignored as it is set during the creation. This commit adds a deprecation
    warning if this option is used.
    
    [1]: https://www.freeipa.org/page/V3/DNS_SOA_serial_auto-incrementation
    [2]: https://www.freeipa.org/page/Releases/3.3.3
    
    Fixes: https://pagure.io/freeipa/issue/8227
    Signed-off-by: Antonio Torres <antorres@redhat.com>
    Reviewed-By: François Cami <fcami@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Rafael Jeffman <rjeffman@redhat.com>