feat(blackjack): implement game start and controls functionality

backend/src/main/java/de/szut/casino/blackjack/BlackJackService.java

@@ -23,6 +23,7 @@ public class BlackJackService {
         BlackJackGameEntity game = new BlackJackGameEntity();
         game.setUser(user);
         game.setBet(betAmount);
+        game.setState("IN_PROGRESS");
 
         for (int i = 0; i < 2; i++) {
             CardEntity playerCard = createRandomCard(game);