Add altSecurityIdentities attribute from MS-WSPP schema definition
    
    Active Directory schema includes altSecurityIdentities attribute
    which presents alternative security identities for a bindable object in
    Active Directory.
    
    FreeIPA doesn't currently use this attribute. However, SSSD certmap
    library may generate searches referencing the attribute if it is
    specified in the certificate mapping rule. Such search might be
    considered unindexed in 389-ds.
    
    Define altSecurityIdentities attribute to allow specifying indexing
    rules for it.
    
    Fixes: https://pagure.io/freeipa/issue/7932
    Related: https://pagure.io/freeipa/issue/7933
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>