Enhance notification system with in-app delivery support

- Added `DeliveryChannelInApp` to support in-app notifications.
- Introduced `EventTypeInApp` constant for identifying in-app notifications.
- Updated `AdminNotifications` and `CustomerNotifications` handlers to set the event type to `EventTypeInApp`.
- Modified the `GetByUserID` repository method to handle filtering for in-app notifications, allowing for more flexible retrieval options.
- Updated the `persistNotification` method to include in-app as a delivery method.

This update improves the notification system by enabling in-app notifications, enhancing user engagement and notification management capabilities.

internal/notification/service.go

@@ -149,7 +149,9 @@ func (s *notificationService) sendToRecipient(ctx context.Context, recipient not
 }
 
 func (s *notificationService) persistNotification(ctx context.Context, recipient notificationRecipient, req *NotificationRequest, link, image string) error {
-	methods := make(map[string]string)
+	methods := map[string]string{
+		"in_app": "true",
+	}
 	if slices.Contains(req.Channels, DeliveryChannelEmail) && recipient.Email != "" {
 		methods["email"] = recipient.Email
 	}
@@ -170,6 +172,7 @@ func (s *notificationService) persistNotification(ctx context.Context, recipient
 		Image:       image,
 		Priority:    string(req.Priority),
 		Type:        string(req.Type),
+		EventType:   EventTypeInApp,
 		Status:      status,
 		Methods:     methods,
 		Metadata: map[string]any{