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/repository.go

@@ -119,13 +119,16 @@ func (r *notificationRepository) GetByID(ctx context.Context, id string) (*Notif
 // GetByUserID retrieves notifications with optional user filters
 func (r *notificationRepository) GetByUserID(ctx context.Context, userIDs []string, search, status string, seen *bool, priority, eventType, notificationType string, pagination *response.Pagination) (*orm.PaginatedResult[Notification], error) {
 	filter := bson.M{}
+	andConditions := bson.A{}
 
 	if q := strings.TrimSpace(search); q != "" {
 		pattern := regexp.QuoteMeta(q)
-		filter["$or"] = bson.A{
-			bson.M{"title": bson.M{"$regex": pattern, "$options": "i"}},
-			bson.M{"message": bson.M{"$regex": pattern, "$options": "i"}},
-		}
+		andConditions = append(andConditions, bson.M{
+			"$or": bson.A{
+				bson.M{"title": bson.M{"$regex": pattern, "$options": "i"}},
+				bson.M{"message": bson.M{"$regex": pattern, "$options": "i"}},
+			},
+		})
 	}
 
 	if len(userIDs) == 1 {
@@ -147,13 +150,31 @@ func (r *notificationRepository) GetByUserID(ctx context.Context, userIDs []stri
 	}
 
 	if eventType != "" {
-		filter["event_type"] = eventType
+		if eventType == EventTypeInApp {
+			andConditions = append(andConditions, bson.M{
+				"$or": bson.A{
+					bson.M{"event_type": EventTypeInApp},
+					bson.M{"event_type": ""},
+					bson.M{"event_type": bson.M{"$exists": false}},
+				},
+			})
+		} else {
+			filter["event_type"] = eventType
+		}
 	}
 
 	if notificationType != "" {
 		filter["type"] = notificationType
 	}
 
+	if len(andConditions) == 1 {
+		for key, value := range andConditions[0].(bson.M) {
+			filter[key] = value
+		}
+	} else if len(andConditions) > 1 {
+		filter["$and"] = andConditions
+	}
+
 	mongoPagination, err := orm.BuildListPagination(
 		pagination.Limit,
 		pagination.Offset,