Feature request: support TLS encrypted Redis connections

Feature request: add support for TLS encrypted Redis connections

With being able to use data-in-transit encryption between MariaDB Server, Maxscale and clients (and between Galera nodes) we should also be able to encrypt communication with the cache backend as this basically has the same information going over the wire as we have between Server/Maxscale and actual clients.

See also: https://redis.io/docs/manual/security/encryption/