Add import/export feature for bookmarks (#14956)

* Add ability to export bookmarks

* Add support for importing bookmarks

* Add bookmark import tests

* Add bookmarks export test

app/controllers/settings/exports/bookmarks_controller.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module Settings
+  module Exports
+    class BookmarksController < BaseController
+      include ExportControllerConcern
+
+      def index
+        send_export_file
+      end
+
+      private
+
+      def export_data
+        @export.to_bookmarks_csv
+      end
+    end
+  end
+end