Refactor OppdragRequest: Change String to KodeEndring enum

Changed the type of `kodeEndring` from String to a new KodeEndring enum to improve type safety and reduce potential errors. Introduced the new KodeEndring enum with values NY, ENDR, and UEND.

libs/data-transfer-objects/src/main/java/no/nav/testnav/libs/dto/oppdragservice/v1/OppdragRequest.java

@@ -28,7 +28,7 @@ public class OppdragRequest {
  private Ompostering ompostering;
  private List<Oppdragslinje> oppdragslinje;
  @NotBlank
- private String kodeEndring;
+ private KodeEndring kodeEndring;
  private KodeStatus kodeStatus;
  private String datoStatusFom;
  @NotBlank
@@ -336,6 +336,12 @@ public enum KodeStatus {
  FEIL;
  }
 
+ public enum KodeEndring {
+ NY,
+ ENDR,
+ UEND
+ }
+
  @Data
  @Builder
  @NoArgsConstructor