Use .ts files for vite config for type safety

i18next-parser.config.ts

@@ -1,4 +1,13 @@
-export default {
+/*
+Copyright 2024 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only
+Please see LICENSE in the repository root for full details.
+*/
+
+import type { UserConfig } from "i18next-parser";
+
+const config: UserConfig = {
   keySeparator: ".",
   namespaceSeparator: false,
   contextSeparator: "|",
@@ -26,3 +35,5 @@ export default {
   input: ["src/**/*.{ts,tsx}"],
   sort: true,
 };
+
+export default config;