Allow interacting with Engine and Service microservices via EventBus

[derevnjuk]

The package should provide the ability to implement a custom event bus that lets clients subscribe to events, execute commands, publish, and receive events, as shown in the diagram above. It makes sense when we have to provide an implementation using several technologies, like RabbitMQ, Redis Stream, or Kafka.

type EventBus interface {
	EventDispatcher
	CommandDispatcher

	register(messageName string, handler EventHandler) error
	unregister(messageName string, handler EventHandler) error
}

The register and unregister methods are used to subscribe to events or unsubscribe from events. Both methods accept only a single argument. The argument is the integration event handler type that is to be executed when the bus receives that corresponding event.

type EventHandler interface {
	Handle(message Message) (any, error)
}

• Define an abstraction for EventBus #20
• Introduce a retry strategy to be used within execute and publish methods #23
• Implement Pub/Sub pattern for RabbitMQ #25
• Implement RPC pattern for RabbitMQ
• Implement HttpCommandDispatcher #26
• Handle transient exceptions based on an exponential backoff retry strategy