Lesson 3 Add Custom Respository Method

Full Changelog: lesson-02...lesson-03

Lesson 2 Testing UserController

What's Changed

• Changed the parent class of UserRepository from CrudRepository to Jpa… by @fuyuko in #1
• Add DeleteAllUsers + AddUser constraint added + Lists operations for JpaRepository by @fuyuko in #3
• simplify the folder structure + simple application sanity check testing by @fuyuko in #4

Full Changelog: lesson-01...lesson-02

Lesson 1

Learned how to implement CRUD operation for User class.