Evaluate data storage and indexing backend for NodeNorm/NodeAnnotator

[gaurav]

We would like to use a single backend for NodeNorm/NodeAnnotator. This may be the current backend (Redis for NodeNorm, with additional database for NodeAnnotator) or another one (ElasticSearch, which is currently used by NodeAnnotator, or PostgreSQL). Johnathan has set up a NodeNorm on ElasticSearch (https://biothings.ci.transltr.io/nodenorm), so we're currently working on evaluating how quickly it responds to queries. @gaurav is working on stress-testing NodeNorm (NCATSTranslator/NodeNormalization#277).