redis cds plug and play modus

[rlindner81]

Similar to changes in
cap-js-community/event-queue#265

The idea is that (when the library runs as a cds-plugin) we let cds handle env resolution, so that it works for cf and kyma. With sensible defaults { vcap: { label: redis-cache }} that can be overridden by cds users as needed.

For reporting the redis mode that the library runs in, we would need to know if cds resolved a local env or not...

I still want the lib to work without cds like before.