[OTLP] include status code in failure log

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/ExportClient/OtlpGrpcExportClient.cs

@@ -93,7 +93,7 @@ public override ExportClientResponse SendExportRequest(byte[] buffer, int conten
                 grpcStatusDetailsHeader = GrpcProtocolHelpers.GetHeaderValue(trailingHeaders, GrpcStatusDetailsHeader);
             }
 
-            OpenTelemetryProtocolExporterEventSource.Log.ExportFailure(this.Endpoint.ToString(), "Export failed due to unexpected status code.");
+            OpenTelemetryProtocolExporterEventSource.Log.ExportFailure(this.Endpoint.ToString(), "Export failed due to unexpected status code.", (int)status.StatusCode);
 
             return new ExportClientGrpcResponse(
                 success: false,

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/OpenTelemetryProtocolExporterEventSource.cs

@@ -208,10 +208,10 @@ public void GrpcStatusWarning(string endpoint, string statusCode)
         this.WriteEvent(22, endpoint, statusCode);
     }
 
-    [Event(23, Message = "Export failed for {0}. Message: {1}", Level = EventLevel.Error)]
-    public void ExportFailure(string endpoint, string message)
+    [Event(23, Message = "Export failed for {0}. Message: {1}. Status code: {2}", Level = EventLevel.Error)]
+    public void ExportFailure(string endpoint, string message, int statusCode)
     {
-        this.WriteEvent(23, endpoint, message);
+        this.WriteEvent(23, endpoint, message, statusCode);
     }
 
     [Event(24, Message = "Failed to parse gRPC retry delay from header grpcStatusDetailsHeader: '{0}'. Exception: {1}", Level = EventLevel.Warning)]