Amazon MemoryDB for Redis adds support for Redis 7

[Amazon MemoryDB for Redis](https://aws.amazon.com/memorydb/) now supports Redis 7\. This release brings several new features to MemoryDB: * Redis Functions: MemoryDB adds support for Redis Functions, and provides a managed experience enabling developers to execute LUA scripts with application logic durably stored on the MemoryDB cluster. * ACL improvements: MemoryDB adds support for the next version of Redis Access Control Lists (ACLs). With MemoryDB, clients can now specify multiple sets of permissions on specific keys or keyspaces in Redis. * Sharded Pub/Sub: MemoryDB now gives you the ability to run Redis’ Pub/Sub functionality in a sharded way. With MemoryDB, channels are bound to a shard in the MemoryDB cluster, eliminating the need to propagate channel information across shards resulting in improved scalability. * Enhanced I/O Multiplexing: MemoryDB now includes enhanced I/O multiplexing, which delivers significant improvements to throughput and latency at scale. As an example, when using r6g.4xlarge node and running 5200 concurrent clients, you can achieve up to 46% increased throughput (read and write operations per second) and up to 21% decreased P99 latency, compared with MemoryDB for Redis 6. Amazon MemoryDB for Redis 7 is available in all regions where MemoryDB is generally available. For more details about MemoryDB, refer to [Supported MemoryDB for Redis versions](https://docs.aws.amazon.com/memorydb/latest/devguide/engine-versions.html#supported-engine-versions). You can upgrade the engine version of your cluster or replication group by modifying it and specifying 7 as the engine version. To learn more about upgrading engine versions, refer to [Version Management](https://docs.aws.amazon.com/memorydb/latest/devguide/engine-versions.html#versionmanagement).