insights: escape whitespace for aggregation drilldown queries

Created by: coury-clark

When author fields have whitespace they will break the semantic of a drilldown query unless whitespace is escaped. For example:

Aggregation query: type:commit insight

Returning drilldown: type:commit author:Santa Claus insight

In reality we need to generate: type:commit author:Santa\ Claus insight or type:commit author:Santa\sClaus insight

/cc @joelkw @felixfbecker @vovakulikov @unclejustin