Feat: Event segregation and permissions

[thantos]

A developer should have control over which events are published outside of the service (service to service subscribe).

When a developer uses service to service subscription, the subscribed events should not be consumed by other subscribers.

graph LR;
   B --subscribes to--> A
   C --subscribes to--> B

• A does not subscribe to any service. It's internal events should not appear in Service B.
• B subscribes to A, it should not get internal events for A, but any non-internal events from A. It's internal events and events from service A should not appear in Service B.
• C subscribes to B, it should only get outgoing events from B and no events from A.

---

• Event Bus already does not support multiple bus hops (A to B to C wouldn't work if we wanted it to)
  • To do this, a consumer needs to manually forward events by re-publishing them as their own events.
• if an Event is not exported from the top of the service, it is considered internal
  • these events can be handled by the service, but a rule cannot be added from outside (see below)
• internal events - have the source eventual:[service name]-jinternalj
• external events (non-internal) - have the source eventual:[service name]
• Add a policy to the bus that says rules created by outside buses must contain the source === [service name]. https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-use-conditions.html
• update subscribe and docs to only use the eventual:[service name] as the source type

---

• Could we just use eventual:service and eventual:service-internal? yes, but it wouldn't be clear to consumers what the service name was. Using the service name allows for further consumer internal routing,
• What stops consumed events from flowing downstream? - EB said it will not do multiple hops and bus to bus rules cannot transform.
• What if a service wants to forward events from another service? this would be a separate feature. It is possible today by creating a handler and using publishEvent