Implement usernameExtract for extracting username

Author: RihannaP

script.js

@@ -1 +1,10 @@
 import express from "express"
+const app = express();
+const port = 3000;
+
+function usernameExtract(req, res, next) {
+  const username = req.get("X-Username");
+  req.username = username ? username : null;
+  next();
+}
+