ES simulator, API docs, Starting on gRPC

[autoencoder]

Progress toward Getty -> blockchain -> indexer ingest -> indexer API output test:

• API Refinements.
• Docs updates.
• WIP setting up artefact ingestion via gRPC.

Indexer model updates:

• ML model refinements.
• Demystifying the Lucene's search relevance scoring function by replicating it - valuable if we continue with the ES inverted index approach. Good for hyper-parameter optimization too. Can now setup testing against a more stable interface.
• Clean up model eval scripts. Generalize eval scripts to handle other datasets.