Summary: Similar to storage.default-namespace sometimes during development you'll want to handle multiple indexes alongside one another. Rather than hardcoding the /phabricator/ index make this exposed in new search.elastic.index setting, defaulting to the existing "phabricator" Test Plan: Existing installations should be unaffected by this change. Changing the new setting will result in new indexes being created when someone runs `./bin/search index` again Reviewers: epriestley, #blessed_reviewers Reviewed By: epriestley, #blessed_reviewers Subscribers: 20after4, rush898, epriestley, Korvin Differential Revision: https://secure.phabricator.com/D9798