fn json_body_parser(output_shape: &str, mutable_result: bool) -> String {
    format!(
        "let {mutable} result = proto::json::ResponsePayload::new(&response).deserialize::<{output_shape}, _>()?;",
        output_shape = output_shape,
        mutable = if mutable_result { "mut" } else { "" }
    )
}
Parse the http response body as a JSON object with serde, and use that
as the result object
service_crategen/src/commands/generate/codegen/rest_json.rs