feat: ReservationStatus enum 내 확정 예약 타입들을 반환하는 메서드 추가

src/main/kotlin/roomescape/reservation/infrastructure/persistence/ReservationEntity.kt

@@ -48,5 +48,10 @@ class ReservationEntity(
 enum class ReservationStatus {
     CONFIRMED,
     CONFIRMED_PAYMENT_REQUIRED,
-    WAITING
+    WAITING,
+    ;
+
+    companion object {
+        fun confirmedStatus(): Array<ReservationStatus> = arrayOf(CONFIRMED, CONFIRMED_PAYMENT_REQUIRED)
+    }
 }