Project: lowdb
Task (easy): 1) create a new api (GET /api/usernames) by creating api route file (app/api/usernames/route.ts)
2) in this api, return a string list in body to get all usernames by User Model (db.data.users), example: ['user1', 'user2']
3) Hint: use global.db.data.users and get user model by lowdb API