File cleanup/organization in controllers/concerns (#27846)

app/controllers/concerns/admin/export_controller_concern.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+module Admin::ExportControllerConcern
+  extend ActiveSupport::Concern
+
+  private
+
+  def send_export_file
+    respond_to do |format|
+      format.csv { send_data export_data, filename: export_filename }
+    end
+  end
+
+  def export_data
+    raise 'Override in controller'
+  end
+
+  def export_filename
+    raise 'Override in controller'
+  end
+
+  def set_dummy_import!
+    @import = Admin::Import.new
+  end
+
+  def import_params
+    params.require(:admin_import).permit(:data)
+  end
+end