feat: add leaderboard api

server/src/api/controllers/leaderboardController.js

@@ -1,5 +1,12 @@
 import { asyncHandler } from '../../middleware/error.js'
+import { leaderboard } from '../../models/userManager.js'
 
 export default asyncHandler(async (req, res) => {
-  res.json({ message: 'leaderboard' })
+  const users = await leaderboard()
+  const response = users.map((user) => ({
+    username: user.user.username,
+    completedQuests: user.completedQuests,
+    numberOfCompletedQuests: user.numberOfCompletedQuests,
+  }))
+  res.json(response)
 })