Add codegen for fhe-benchmarking.org

We had discussed this previously offline, but with the new FHE benchmarking system online, it would be nice to have a means for HEIR to generate the boilerplate required for submitting to fhe-benchmarking.org.

Details about the project are here: https://github.com/fhe-benchmarking

The [MNIST reference example](https://github.com/fhe-benchmarking/ml-inference/tree/main/submission) in that repo had the main code generated by HEIR, but the boilerplate was added manually.