fix: disable async mode by default

Author: oliemansm

graphql-spring-boot-autoconfigure/src/main/java/graphql/kickstart/autoconfigure/web/servlet/AsyncServletProperties.java

@@ -12,7 +12,7 @@ public class AsyncServletProperties {
 
   public static final Duration DEFAULT_TIMEOUT = Duration.ofSeconds(30);
 
-  private boolean enabled = true;
+  private boolean enabled = false;
   /**
    * Asynchronous execution timeout. If a duration suffix is not specified, millisecond will be used.
    */