[feature req] Switch Faiss to ScaNN

[ldmtwo]

I suggest the change because of benchmarks. I've found it easy and agree with the bench.

https://github.com/google-research/google-research/tree/master/scann

the-algorithm/ann/src/main/python/dataflow/faiss_index_bq_dataset.py

Thanks for uploading all this free education. I've learned so much in a few hours.