added the GET /teachers (#130)

had to fix the mock and the UserController isAdminOrSecretary

Reviewed-on: #130
Reviewed-by: Wal <karpinskiwal@gmail.com>
Reviewed-by: Debucquoy Anthony <d.tonitch@gmail.com>
Co-authored-by: Bartha Maxime <231026@umons.ac.be>
Co-committed-by: Bartha Maxime <231026@umons.ac.be>

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

@@ -103,4 +103,8 @@ public class UserService {
     public Iterable<User> getAll(){
         return userRepo.findAll();
     }
+
+
+
+    public Iterable<User> getAllTeachers (){return userRepo.findAllTeachers();}
 }