When documents are indexed, record the indexer version (versus the object version) and index epoch
Make it easier to reindex a subset of documents (based on the date when the index was built, and/or the software version which generated the index).
This is in addition to the existing versioning, which is focused on object versions.
Test Plan: Ran bin/search index with various old and new arguments. Spot-checked the IndexVersion table.
Maniphest Tasks: T13587
Differential Revision: https://secure.phabricator.com/D21560