Add AccountsAPIError class and productvoucher route

Introduces a custom AccountsAPIError class for consistent error handling and serialization. Adds a new /productvoucher/giftcode route that returns a 404 error response for unimplemented endpoints.

routes/minecraftservices/productvoucher.js

@@ -0,0 +1,14 @@
+const express = require("express")
+const router = express.Router()
+
+router.get("/giftcode", (req, res) => {
+    res.status(404).json({
+        path: "/productvoucher/giftcode",
+        errorType: "NOT_FOUND",
+        error: "NOT_FOUND",
+        errorMessage: "The server has not found anything matching the request URI",
+        developerMessage: "The server has not found anything matching the request URI"
+    })
+})
+
+module.exports = router