Update Reference Architecture docs with guidance on Redis LRU Cache

A small omission for the Reference Architecture docs is the configuration for Redis Cache to be used as a LRU Cache as detailed here in other docs.

In a nutshell the docs need to be updated to say for the Redis Cache instances the additional config is needed:

redis['maxmemory'] = '<90% of available ram in MB>'
redis['maxmemory_policy'] = "allkeys-lru"
redis['maxmemory_samples'] = 5