Add ListRepoNames method to Repo Store
Created by: asdine
This PR adds a new Repo store method called ListRepoNames
that only lists repo names (and ids) rather than returning the entire repo.
The goal of this method is to be used whenever we don't need to fetch complete repository information (especially important for Search code).
Currently, this method scans 6 fields instead of just the repo ID and Name. Subsequent PRs will change that behaviour from within the getReposBySQL
method, and unexport the OnlyRepoIDs
option.
Part of https://github.com/sourcegraph/sourcegraph/issues/16219