Add design document
    
    This document details authentication indicaters and kerberos ticket
    policies implemented in IPA.
    
    Resolves: https://pagure.io/freeipa/issue/8001
    Signed-off-by: Changmin Teng <cteng@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Simo Sorce <ssorce@redhat.com>
    Reviewed-By: Robbie Harwood <rharwood@redhat.com>