public ReservationService(EasyRehearsalManagerContext context, UserManager <User> userManager)
 {
     _context     = context;
     _userManager = userManager;
     _reservationDateValidator = new ReservationDateValidator(_context);
 }
        //private readonly IReservationService _reservationService;

        public ReservationDateValidator(EasyRehearsalManagerContext context)
        {
            _context = context; //itt is inkább a reservationService-t kéne használni
            //_reservationService = reservationService;
        }