feature_flags: Default-enable use of filtered quarantine commits

With 4aba970e (gitaly_client: Allow filtering quarantined commits by existence, 2022-05-03), we have introduced code that enables us to use the repo's quarantine directory in order to enumerate commits in access checks. This can lead to a significant speedup when enumerating commits in repositories which have a lot of references because the previous way of enumerating commits would require us to walk each of the preexisting refs so that we can find the commits that really are new.

We have rolled the accompanying feature flag without any observed issues so far, so let's default-enable the feature flag.

Part of #361174 (closed)