Passkey: add a weak dependency on sssd-passkey
    
    The package sssd-passkey provides the executable
    /usr/libexec/sssd/passkey_child
    which is not mandatory but recommended.
    
    Add a weak dependency from ipa client package on sssd-passkey.
    
    TBD: when a new version of sssd is released with passkey
    support, bump the SSSD version.
    
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>