SDAP: Add request that iterates over all search bases
    
    We often need to iterate over many search bases but we always use
    mostly copy&paste iterator. This will reduce code duplication and
    simplify code flow.
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>
    (cherry picked from commit d0599eaa9369fd867953e3c58b8d7bb445525ff5)