Elasticsearch: look at changing `termAggregation.shardSize` to be a function of requested terms

[joeferner]

https://github.com/visallo/vertexium/blob/master/elasticsearch5/src/main/java/org/vertexium/elasticsearch5/ElasticsearchSearchIndexConfiguration.java#L25

By setting termAggregation.shardSize to a specific value this limits requests with larger requested terms.

So if you ask for 100 terms, 10 is too small.

If instead we change this to a function of the requested terms this could accommodate more requests. Possibly 2 times the number of requested terms.