Function dataflow::render::sources::flatten_results_prepend_keys

fn flatten_results_prepend_keys<G>(
    key_envelope: &KeyEnvelope, 
    results: Stream<G, KV>
) -> Stream<G, Result<Row, DecodeError>> where
    G: Scope<Timestamp = Timestamp>, 

Convert from streams of DecodeResult to Rows, inserting the Key according to KeyEnvelope