feat: implement event notification system

- Add core event notification interfaces
- Support multiple notification backends:
  - Webhook (default)
  - Kafka
  - MQTT
  - HTTP Producer
- Implement configurable event filtering
- Add async event dispatching with backpressure handling
- Provide serialization/deserialization for event payloads

This module enables system events to be published to various endpoints
with consistent delivery guarantees and failure handling.

crates/event-notifier/examples/.env.example

@@ -0,0 +1,27 @@
+# basic configuration
+EVENT_NOTIF_STORE_PATH=/var/log/event-notification
+EVENT_NOTIF_CHANNEL_CAPACITY=5000
+
+# webhook adapter configuration
+EVENT_NOTIF_ADAPTERS__0__TYPE=Webhook
+EVENT_NOTIF_ADAPTERS__0__ENDPOINT=https://api.example.com/webhook
+EVENT_NOTIF_ADAPTERS__0__AUTH_TOKEN=your-secret-token
+EVENT_NOTIF_ADAPTERS__0__MAX_RETRIES=3
+EVENT_NOTIF_ADAPTERS__0__TIMEOUT=5000
+
+# kafka adapter configuration
+EVENT_NOTIF_ADAPTERS__1__TYPE=Kafka
+EVENT_NOTIF_ADAPTERS__1__BROKERS=localhost:9092
+EVENT_NOTIF_ADAPTERS__1__TOPIC=notifications
+EVENT_NOTIF_ADAPTERS__1__MAX_RETRIES=3
+EVENT_NOTIF_ADAPTERS__1__TIMEOUT=5000
+
+# mqtt adapter configuration
+EVENT_NOTIF_ADAPTERS__2__TYPE=Mqtt
+EVENT_NOTIF_ADAPTERS__2__BROKER=mqtt.example.com
+EVENT_NOTIF_ADAPTERS__2__PORT=1883
+EVENT_NOTIF_ADAPTERS__2__CLIENT_ID=event-notifier
+EVENT_NOTIF_ADAPTERS__2__TOPIC=events
+EVENT_NOTIF_ADAPTERS__2__MAX_RETRIES=3
+
+EVENT_NOTIF_HTTP__PORT=8080