XD-2061 Add Redis sink module

 - Add Redis sink with the following options:
    - topic (a SpEL expression)
    - hostname, port and password
@ericbottard once you set `sink.redis.key` to `foo` then you would expect to see the default value for **key** only. Setting it for `keyExpression` is implementation specific and I don't think we need to show that to end user.