add paginator

lib/domain/constants.dart

@@ -10,6 +10,7 @@ const delivery_address_collection = "delivery_addresses";
 const cargo_types_collection = "cargo_types";
 const custom_duties_collection = "custom_duties";
 const discounts_by_weights_collection = "discounts_by_weight";
+const shipments_collection = "shipments";
 
 // docs
 const setting_doc_id = "setting";