aws-elasticache-audit — find the ElastiCache groups that cannot lose a node

Everybody calls ElastiCache a cache right up to the morning it holds the only copy of every live session. aws-elasticache-audit reads every replication group and cache cluster once and says which of them cannot survive losing one node: failover disabled, a single availability zone, encryption off, no auth token, zero snapshot retention and engine versions past end of support.