feat: make dto classes final

src/main/java/cz/muni/fi/pa165/icehockeymanager/dto/PlayerDTO.java

@@ -7,7 +7,7 @@ import javax.validation.constraints.NotBlank;
 import javax.validation.constraints.NotNull;
 import java.util.Objects;
 
-public class PlayerDTO {
+public final class PlayerDTO {
     @NotNull
     @Getter
     @Setter

src/main/java/cz/muni/fi/pa165/icehockeymanager/dto/TeamDTO.java

@@ -7,7 +7,7 @@ import javax.validation.constraints.NotBlank;
 import javax.validation.constraints.NotNull;
 import java.util.Objects;
 
-public class TeamDTO {
+public final class TeamDTO {
     @NotNull
     @Getter
     @Setter