R1:0f144d29e920

When "cluster.search" changes, don't trust the old index versions

Summary:
Ref T12450. We track a "document version" for updating search indexes, so that if a document is rapidly updated many times in a row we can skip most of the work.

However, this version doesn't consider "cluster.search" configuration, so if you add a new service (like a new ElasticSearch host) we still think that every document is up-to-date. When you run `bin/search index` to populate the index (without `--force`), we just do…