ipa-pwd-extop: declare operation notes support from 389-ds locally
    
    The function slapi_pblock_set_flag_operation_notes(); is defined in
    ldap/servers/slapd/pblock.c in 389-ds but is only available through
    slapi-private.h header, not through slapi-plugin.h public API.
    
    It was introduced in ~1.4.1.7 (~2019) via https://pagure.io/389-ds-base/issue/50349.
    
    Since we only use it with an MFA note, all versions of the 389-ds that
    will support MFA note will have this function.
    
    Fixes: https://pagure.io/freeipa/issue/9554
    
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>