Update mvc-ann-async.adoc

Added a section explaining WebAsyncTask return type along with java and kotlin example code. Signed-off-by: addoDev <211474908+addoDev@users.noreply.github.com>

Author: addoDev

framework-docs/modules/ROOT/pages/web/webmvc/mvc-ann-async.adoc

@@ -99,7 +99,7 @@ xref:web/webmvc/mvc-ann-async.adoc#mvc-ann-async-configuration-spring-mvc[config
 [[mvc-ann-async-webasynctask]]
 == `WebAsyncTask`
 
-`WebAsyncTask` is a holder/wrapper for a `java.util.concurrent.Callable` that allows you set a custom asynchronous request  timeout value and a custom `AsyncTaskExecutor` for executing the `java.util.concurrent.Callable` if you want to use a  different `AsyncTaskExecutor` than the default one used by Spring MVC. Below is an example of using `WebAsyncTask`:
+`WebAsyncTask` is a holder/wrapper for a `java.util.concurrent.Callable` that allows you to set a custom asynchronous request timeout value and a custom `AsyncTaskExecutor` for executing the `java.util.concurrent.Callable` if you want to use a different `AsyncTaskExecutor` than the default one used by Spring MVC. Below is an example of using `WebAsyncTask`:
 
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