Add NATS as a Receiver

[latchmihay]

Would it be possible to add NATS support to the receivers? It would be great if NATS can be used as notifier (already completed) and as a receiver provider allowing bidirectional notification messaging and ultimately kicking off reconciliation loops.

I see ArgoCD have already implemented this capability

[latchmihay]

After further reading I realized that the notification controller Receivers work by starting an HTTP endpoint which parse the payloads it received from its supported Receiver Types.

This paradigm is not compatible with NATS.

Perhaps such functionality is better suited for a separate controller or an introduction of new notification-controller kind such as ExternalEvents that could handle subscribing to messages and triggering reconciliations on Flux Resources.

This type of implementation would allow for use-cases like cron, pub/sub, and streams to trigger Flux Resource reconciliations nativity.