Feature: Nats support for pub sub uses.

[joeblew999]

Currently pub sub uses Kafka .

For example : https://github.com/block/ftl/blob/main/backend/runner/pubsub/consumer.go

Nats Jetstream would be another one and it also has partitioning these days.

We could also add tooling to use an embedded nats server as an option to help with dev and testing if we wish too.

Nats is getting corn jobs too soon , but that is orthogonal to this issue .

[joeblew999]

Also would need to add tooling TF in https://github.com/block/ftl/tree/main/tf/modules/sandbox for nats server , as all the sub systems are there as Terraform

[joeblew999]

also need to account for Redpanda to use nats .
Not sure if this is at control plane or data plane usage .