search: register repogroup routes in frontend

Created by: keegancsmith

This is to prevent us 404ing when loading a repogroup page. This is copying the hack in the webapp currently and is not sufficient for when we roll this out. Instead the repogroups should be living under a subpath, rather than top-level paths.

Additionally the current logic in the webapp is just a string contains, so registers many more paths. From testing thankfully our frontend prefers paths that match repos.

Part of https://github.com/sourcegraph/sourcegraph/issues/11922