add GitserverReposStore to repo.Store
Created by: mollylogue
Update the GitserverRepoStore
to make it an interface (i.e. similar to RepoStore
) and add to repo.Store
. Doing this as a precursor to https://github.com/sourcegraph/sourcegraph/pull/28522 in which we need to have access to the gitserver_repos
table to check last_error
but splitting this update into a separate PR for ease of review.
Part of https://github.com/sourcegraph/sourcegraph/issues/25217 (which will be fixed by several PRs)