Design: Integrate SID configuration into base IPA installers
    
    Add design doc for the feature.
    
    Related: https://pagure.io/freeipa/issue/8995
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>