Fix setup of OLTP exporter condition in sample

Author: kzu

sample/ServiceDefaults.cs

@@ -71,7 +71,7 @@ public static TBuilder ConfigureOpenTelemetry<TBuilder>(this TBuilder builder)
             });
 
 
-        if (string.IsNullOrWhiteSpace(builder.Configuration["OTEL_EXPORTER_OTLP_ENDPOINT"]))
+        if (!string.IsNullOrWhiteSpace(builder.Configuration["OTEL_EXPORTER_OTLP_ENDPOINT"]))
             builder.Services.AddOpenTelemetry().UseOtlpExporter();
 
         return builder;