Extend the list of supported pre-auth mechanisms in IPA server API
    
    As new authentication indicators implemented, we also modified server
    API to support those new values. Also, "krbprincipalauthind" attribute
    is modified to use a pre-defined set of values instead of arbitrary
    strings.
    
    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>