feat: add import headers to export instance

lib/tallty_import_export/import.rb

@@ -49,9 +49,10 @@ module TalltyImportExport
 
     def export_workbook(workbook, **options)
       export_instance = TalltyImportExport::Export.new(@klass)
-      Rails.logger.info options.symbolize_keys
-      export_instance.process_options(options.symbolize_keys)
-      export_instance.export_workbook(workbook, [], **options.symbolize_keys)
+      opts = options.symbolize_keys.merge({ headers: @headers })
+      Rails.logger.info opts
+      export_instance.process_options(opts)
+      export_instance.export_workbook(workbook, [], **opts)
     end
 
     def exchange_to_ids(xlsx_file, associations, **options)