Support Redis client side caching

[gdarmont]

Is your feature request related to a problem? Please describe.
Flags and properties are usually way more retrieved than modified. Using a distributed cache like Redis helps avoiding querying the persistent store, but on a high workload application, it still triggers a lots -sometimes tens of thousands- of GET queries to only have the same value each time.

Describe the solution you'd like
Redis 6 offers a way to implement client side caching : see https://redis.io/docs/manual/client-side-caching/
This would helps FF4J to not trigger remote call to Redis server for every flag or property check, while having a near-realtime invalidation of the client side cache entries.

Describe alternatives you've considered
One current solution is to chain FF4jCacheProxy, i.e. have a FF4jCacheProxy using InMemoryCacheManager over a FF4jCacheProxy using FF4jCacheManagerRedis. But in that case, even with a low TTL on the InMemoryCacheManager, we lose the fact that a new value is seen ASAP.