[discovery] Add Top Hits Aggregation

[maniax89]

Description

Feature Request: Add in the top_hits aggregation enum for a discovery QueryRequest . The spec can be found at http://www.ibm.com/watson/developercloud/doc/discovery/query-reference.shtml#aggregrations

Excerpt:

Returns the documents ranked by the score of the query or enrichment. Can be used with any query parameter or aggregation. This example returns the 10 top hits for a term aggregation.

Example:

term(enriched_text.concepts.text).top_hits(10)

Solution

• [ ] add TOP_HITS to the AggregationType enum in the com.ibm.watson.developer_cloud.discovery.v1.model.query package.
• [ ] create the proper deserialization of the response in the com.ibm.watson.developer_cloud.discovery.v1.model.query.QueryAggregationAdapterFactory class as well as create the appropriate models that extend the com.ibm.watson.developer_cloud.discovery.v1.model.query.QueryAggregation class (see Calculation aggregation for example)
• [ ] write a test that ingests a JSON document and then uses the new TOP_HITS aggregation to create top_hits aggregation chained after a term aggregation

When you open an issue for a feature request, please add as much detail as possible:

• [x] A descriptive title starting with the service name
• [X] A description of the problem you're trying to solve
• [X] A suggested solution if possible

[pbwilmot]

I agree this would be very helpful