feat(event-notifier): improve environment variable handling

- Fix deserialization error when parsing config from environment variables
- Add proper array format support for adapters configuration
- Update environment variable examples with correct format
- Improve documentation for configuration loading
- Implement helper functions for environment variable validation

This change fixes the "invalid type: map, expected a sequence" error
by ensuring proper formatting of array-type fields in environment variables.

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

@@ -1,27 +1,28 @@
-# basic configuration
-EVENT_NOTIF_STORE_PATH=/var/log/event-notification
-EVENT_NOTIF_CHANNEL_CAPACITY=5000
+# ===== global configuration =====
+NOTIFIER__STORE_PATH=/var/log/event-notification
+NOTIFIER__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
+# ===== adapter configuration array format =====
+# webhook adapter index 0
+NOTIFIER__ADAPTERS_0__type=Webhook
+NOTIFIER__ADAPTERS_0__endpoint=http://127.0.0.1:3000/webhook
+NOTIFIER__ADAPTERS_0__auth_token=your-auth-token
+NOTIFIER__ADAPTERS_0__max_retries=3
+NOTIFIER__ADAPTERS_0__timeout=50
+NOTIFIER__ADAPTERS_0__custom_headers__x_custom_server=server-value
+NOTIFIER__ADAPTERS_0__custom_headers__x_custom_client=client-value
 
-# 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
+# kafka adapter index 1
+NOTIFIER__ADAPTERS_1__type=Kafka
+NOTIFIER__ADAPTERS_1__brokers=localhost:9092
+NOTIFIER__ADAPTERS_1__topic=notifications
+NOTIFIER__ADAPTERS_1__max_retries=3
+NOTIFIER__ADAPTERS_1__timeout=60
 
-# 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
+# mqtt adapter index 2
+NOTIFIER__ADAPTERS_2__type=Mqtt
+NOTIFIER__ADAPTERS_2__broker=mqtt.example.com
+NOTIFIER__ADAPTERS_2__port=1883
+NOTIFIER__ADAPTERS_2__client_id=event-notifier
+NOTIFIER__ADAPTERS_2__topic=events
+NOTIFIER__ADAPTERS_2__max_retries=3