This introduces a new manager stats method, `LocalSiteManager.get_local_site_acl_stats()`. This returns a dictionary containing: 1. The number of users on the Local Site 2. The number of admins on the Local Site 3. Whether the Local Site is public 4. A UUID representing the generated state (which can be used as a component of other cache keys to enable automatic invalidation) This is per-Local Site. It exists on the manager so that either a pre-fetched `LocalSite` instance can be provided, or the primary key of a `LocalSite`. That makes it usable in methods where we may not yet want to fetch a `LocalSite`. This information is cached. It's invalidated whenever user/admin membership changes, when `public` does or may have changed (based on whether `LocalSite.save()` is called with/without `update_fields=`), or when a `LocalSite` is deleted. This will soon be used by other query-generating code to conditionally fetch data from the database, and as components for other cache keys.