feat: extract booking session handling

tests/Service/BookingServiceBabyTest.php

@@ -13,6 +13,7 @@ use App\Form\Model\BookingDto;
 use App\Form\Model\ParticipantDto;
 use App\Service\BookingPriceCalculatorService;
 use App\Service\BookingService;
+use App\Service\BookingSessionService;
 use App\Service\ParticipantEligibilityService;
 use App\Service\TravelDataService;
 use PHPUnit\Framework\TestCase;
@@ -32,6 +33,7 @@ class BookingServiceBabyTest extends TestCase
         $agencyLoader = $this->createMock(AgencyLoader::class);
 
         $this->bookingService = new BookingService(
+            $this->createMock(BookingSessionService::class),
             $travelDataService,
             $priceCalculator,
             $this->participantEligibilityService,