search: aggregate RepoURLs from zoekt replicas

Created by: keegancsmith

When horizontal search was released this was assumed to be an unused field. However, the repohasfile filter uses it. Not aggregating leads to repohasfile filtering to always getting an empty set. So when using repohasfilter you would never get any repos. When using -repohasfilter you would get all repos. This is a regression since 3.10.

Fixes https://github.com/sourcegraph/sourcegraph/issues/7380