Add NATS request/reply pattern processor

[marshauf]

Adds a Benthos processor component, which allows sending request to a NATS subject and awaits a response.

Based on the concept of https://docs.nats.io/nats-concepts/core-nats/reqreply

Developed alongside https://github.com/benthosdev/benthos/pull/2352 and I am also happy to hear any feedback.