search: Zoekt sends list of indexed repos when requesting what to index
Created by: keegancsmith
Previously there was a race condition when computing the list of repositories to index. We try to avoid dropping repos that are already indexed by a node if no other node has indexed it. We did this by asking zoekt-webserver the list of repos. However, zoekt-indexserver may ask for the list of repos before zoekt-webserver has started => this list being empty.
This resolves this comment https://github.com/sourcegraph/sourcegraph/pull/6277#discussion_r340840535
Test plan: CI and testing locally DEV_SEARCH_SHARDING=t dev/launch.sh
Part of https://github.com/sourcegraph/sourcegraph/issues/5725