Include an application key in the storage key

[liwp]

At the moment rate limit keys (in Redis, but this would apply to other shared storage backends as well) include congestion, the limit type name, and the limit id. Eg an IP rate limit key in Redis looks like this:

congestion-congestion.limits.IpRateLimit:limit-id-80.41.61.22

This means that there's a chance of key name collisions if multiple applications want to use a single Redis instance to store their rate limit counters.

By including an application key in the key name we could guarantee that multiple applications can use the same storage server without the risk of name collision.