add a parallel variable with default config (#278)

Author: zhongkechen

sdk/src/main/java/software/amazon/lambda/durable/DurableContext.java

@@ -518,6 +518,15 @@ default <I, O> DurableFuture<MapResult<O>> mapAsync(
     <I, O> DurableFuture<MapResult<O>> mapAsync(
             String name, Collection<I> items, TypeToken<O> resultType, MapFunction<I, O> function, MapConfig config);
 
+    /**
+     * Creates a {@link ParallelDurableFuture} for executing multiple branches concurrently with default config
+     *
+     * @return a new ParallelDurableFuture for registering and executing branches
+     */
+    default ParallelDurableFuture parallel(String name) {
+        return parallel(name, ParallelConfig.builder().build());
+    }
+
     /**
      * Creates a {@link ParallelDurableFuture} for executing multiple branches concurrently.
      *