Adds external_notifications field to BidResponse (#136)

* adds external_notifications field to BidResponse

kotlin/src/commonMain/kotlin/com/adsbynimbus/openrtb/response/BidResponse.kt

@@ -31,6 +31,7 @@ import kotlin.jvm.JvmStatic
  * @property position The position from the request for this ad.
  * @property trackers Contains additional tracking urls for measurement.
  * @property duration The duration in seconds or 0 if unknown or another ad type.
+ * @property external_notifications Contains urls used to notify external services.
  */
 @Serializable
 public class BidResponse(
@@ -51,11 +52,16 @@ public class BidResponse(
     @JvmField @SerialName("position") public val position: String,
     @JvmField @SerialName("trackers") public val trackers: Map<String, Array<String>> = emptyMap(),
     @JvmField @SerialName("duration") public val duration: Int = 0,
+    @JvmField @SerialName("external_notifications") public val external_notifications: Map<String, String> = emptyMap(),
 ) {
     /** Urls to fire a request to when an impression is registered */
     public val impression_trackers: Array<String>? get() = trackers["impression_trackers"]
     /** Urls to fire a request to when a click is registered */
     public val click_trackers: Array<String>? get() = trackers["click_trackers"]
+    /** Url to fire a request to when an there's an auction win */
+    public val win_response: String? get() = external_notifications["win_response"]
+    /** Url to fire a request to when an there's an auction loss */
+    public val loss_response: String? get() = external_notifications["loss_response"]
 
     public companion object {
         /** Decodes a BidResponse from a Json string using the built in serializer */