OAK-1966 - Add Hint for selecting more performant index in MongoDocumentStore#query

Merged rev 1611021 from trunk. Disabling this feature by default for now


git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1611022 13f79535-47bb-0310-9956-ffa450edef68