add issue documentation

Author: brendenehlers

sdk-extensions/autoconfigure/src/main/java/io/opentelemetry/sdk/autoconfigure/AutoConfiguredOpenTelemetrySdkBuilder.java

@@ -637,6 +637,7 @@ Thread shutdownHook(OpenTelemetrySdk sdk) {
           try {
             sdk.close();
           } catch (NoClassDefFoundError e) {
+            // https://github.com/open-telemetry/opentelemetry-java/issues/6827
             if (IS_MAVEN) {
               // logging deps might not be on the classpath at this point
               System.out.printf("%s Flush failed during shutdown: %s%n", Level.WARNING, e);