Ensure stored client metadata values respect constraints

src/modules/downloads/Downloads.constants.ts

@@ -0,0 +1,14 @@
+/*
+ * Copyright (C) Contributors to the Suwayomi project
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+export const DOWNLOAD_AHEAD = {
+    min: 2,
+    max: 10,
+    default: 2,
+    step: 1,
+};