Rack::Attack needs a better way of alerting us if it's failed or succeeded!

[KludgeKML]

Currently we just have Rack::Attack on the defaultish settings for throttling requests. But that gives us no oversight on when throttling is happening, and we also don't have an alert if the throttling is disabled on startup either by the explicit DISABLE_THROTTLE var being set or by there being no REDIS_URL.

Perhaps the rate-limit state could go into the health check (although that's public, and maybe we don't want to advertise whether the rate-limit is turned on?). We could maybe have a specific rate-limit health check that Smokey can call, using the rate-limit-token as an accessor?