added GET /user/{id}

backend/src/main/java/ovh/herisson/Clyde/Services/UserService.java

@@ -122,4 +122,8 @@ public class UserService {
     public Iterable<User> getAllTeachers (){return userRepo.findAllTeachers();}
 
     public Iterable<User> getAllStudents(){return userRepo.findAllStudents();}
+
+    public User getUserById(long id) {
+        return userRepo.findById(id);
+    }
 }