Create an index on harbormaster_buildlog to reduce page load times
Summary: Resolves T5895. This reduces page load times significantly when looking at builds.
Test Plan: Viewed a build, saw the page load a lot faster.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: epriestley, Korvin
Maniphest Tasks: T5895
Differential Revision: https://secure.phabricator.com/D10286