Simple Tenant Usage Pagination Support

The simple tenant usage API can return extremely large amounts of data and provides no way to paginate the results. Because the API does not use the pagination code, it doesn't even respect the "max results" sanity limit. Because it can query a ton of data, it also causes the api workers to inflate their memory footprint to the size of the DB result set, which is large. Since horizon queries this by default, most users are affected unless their ops team is extremely diligent about purging deleted instances (which are returned by the API by design).