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/src/error.rs

@@ -1,3 +1,4 @@
+use config::ConfigError;
 use thiserror::Error;
 use tokio::sync::mpsc::error;
 use tokio::task::JoinError;
@@ -35,7 +36,7 @@ pub enum Error {
     #[error("Configuration error: {0}")]
     ConfigError(String),
     #[error("Configuration loading error: {0}")]
-    Figment(#[from] figment::Error),
+    Config(#[from] ConfigError),
 }
 
 impl Error {