gitserver: Reclone repositories with gic gc warnings

Created by: keegancsmith

45 days is too long to wait for large repositories such as kubernetes. Git will add a warning log file called gc.log when it detects a clone is needed. Our reclone job now takes this signal into account when deciding to reclone. If the file is present and it has been at least a day since our last clone, the repository will get recloned.

Test Plan: unit tests

Fixes https://github.com/sourcegraph/sourcegraph/issues/5522