T7827: Boost Elasticsearch results on title match.

Summary: If match is found on document title, boost result.

Test Plan:

• Setup phabricator with elasticsearch.
• Index documents with bin/search index --all
• Use search and expect query matching titles appear on the top of results list.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: WikiChad, Korvin, epriestley

Maniphest Tasks: T7827

Differential Revision: https://secure.phabricator.com/D12432