zoekt: indexserver removes repos from queue
Created by: keegancsmith
This includes several changes to zoekt indexserver which improve observability as well as make us behave better during rebalancing. In particular we would try to index all repos on a replica if we ever rebalanced. We will still do that, but as soon as the replica comes back up we will stop doing that.
- https://github.com/sourcegraph/zoekt/commit/3e5f0f3 indexserver: track last index state as a metric
- https://github.com/sourcegraph/zoekt/commit/cfdfeff indexserver: metrics for queue
- https://github.com/sourcegraph/zoekt/commit/a453878 indexserver: stop indexing repositories if not listed