feat(config): integrate etcd for service discovery and config management

- Add etcd-client dependency for distributed configuration storage
- Implement EtcdConfig with priority: etcd > environment variables > defaults
- Add ServiceRegistry for service registration with lease keep-alive
- Integrate etcd-based service discovery for appks gRPC connections
- Add service watcher for real-time service instance updates
- Migrate Redis configuration from single URL to cluster node list
- Update Dockerfile with default IMKS_HOST and IMKS_PORT environment variables
- Add etcd bootstrap configuration through environment variables
- Implement Redis cluster URL building with optional authentication

svc/scheduled.rs

@@ -34,8 +34,7 @@ impl MessageService {
         let thread_id: Option<Uuid> = Self::parse_optional(payload, "thread_id")?;
         let reply_to_message_id: Option<Uuid> =
             Self::parse_optional(payload, "reply_to_message_id")?;
-        let metadata: Option<serde_json::Value> =
-            Self::parse_optional(payload, "metadata")?;
+        let metadata: Option<serde_json::Value> = Self::parse_optional(payload, "metadata")?;
         let scheduled_at_str: String = Self::parse_field(payload, "scheduled_at")?;
 
         let scheduled_at: DateTime<Utc> = chrono::DateTime::parse_from_rfc3339(&scheduled_at_str)