[Proposal] Create an adapter to use PubSub components as Bindings

Currently, there are several bindings that have a pubsub counterpart (E.g. Kafka, Rabbit, Pulsar, NATS, Redis). In many cases the code in the PubSub component is far more robust. Given the similarity between bindings (Data + Metadata) and pubsub (Topic + Data + Metadata), an adapter could be used that specifies the read/invoke topics to subscribe and publish to. The primary motivation is that adapter reuses code and users can expect the same behavior between the binding and pubsub.

Here are some issues that would possibly be resolved for Kafka:

#1277
#1084
#955
#1006
#168

The downside is that if there are current inconsistencies in the component settings, then migrating to this approach would break existing versions. Since none of these components are marked as stable (yet), now is the time to do this if at all.