Namespace redis keys per connection client

We need to enforce proper namespacing across redis connection objects to prevent eventual collision between clients such as sidekiq and message_bus.

This is an alternative to https://github.com/3scale/3scale-operator/pull/114, allowing all system redis connections to share the same redis instance/db by default.

This can be achieved by using the redis-namespace gem (already bundled with system). Example: https://github.com/3scale/porta/blob/65831a6e992b35c8c4efa0bd2fad5e99e02fdf6b/app/lib/three_scale/timed_value.rb#L18