feat: add export_template_xlsx to importable

lib/tallty_import_export/importable.rb

@@ -28,6 +28,10 @@ module TalltyImportExport
       def exchange_to_ids xlsx_file, associations, **options
         import_instance.exchange_to_ids(xlsx_file, associations, **options)
       end
+
+      def export_template_xlsx **options
+        import_instance.export_template_xlsx(**options)
+      end
     end
   end
 end