FORUM-692 [Unified Search] DiscussionSearchConnector doesn't show result after INTEG-249

Problem analysis
* DiscussionSearchConnector needs to encode the keyword before querying.
  It uses Lucene fuzzy search with explicit similarity value while Unified Search doesn't explicit this value.
* INTEG-249 allows to enable/disable fuzzy option, Discussion Search Connector has to update the query builder.

Fix description
* Update the query builder to handle correctly the fuzzy search setting of Unified Search.