Just another use case to test. This is supposed to be the desired
mode for core-middleware, so we should at least have this tested as
chances are high that admins want to align on the redis deployment.

This is a breaking change.

Changelog:
- Redis is now mandatory and enabled by default
- Added Sentinel, Standalone and Cluster support
- Standalone mode with sidecar is used by default
  - If no host(s) are configured, a redis sidecar is injected into the deployment
  - No extra configuration needed
  - This is intended for development and does not scale.
- Helm values have changed, see README.md:
  - `redis.host` has been renamed to `redis.hosts` and expects a list of strings with the following pattern: <localhost:6379> (needed for sentinel and cluster modes)
  - `redis.port` has been removed, see `redis.hosts`

fix deployments that did not have this value configured at all
by providing a sensible default.

(see OXUI-1015)