Prevents DNS Amplification Attack and allow to customize named
    
    While [1] did open recursion, it also opened widely a security flaw.
    
    This patch intends to close it back, while allowing operators to easily
    add their open configuration within Bind9.
    
    In order to allow operators to still open Bind recursion, a new file is
    introduced, "ipa-ext.conf" (path might change according to the OS). This
    file is not managed by the installer, meaning changes to it won't be
    overridden.
    Since it's included at the very end of the main configuration file, it
    also allows to override some defaults - of course, operators have to be
    careful with that.
    
    Related-Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1754530
    Fixes: https://pagure.io/freeipa/issue/8079
    
    [1] https://github.com/freeipa/freeipa/commit/5f4c75eb28b3d50a35fbf3a86a6d842bce8e72f9
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Stanislav Levin <slev@altlinux.org>