Add async native Java Client (#4721)

* Add async native Java Client

* UPDATE: Reformat the samples

* test java native async in drone.io

* update test count

Co-authored-by: William Cheng <wing328hk@gmail.com>

samples/client/petstore/java/native-async/docs/XmlItem.md

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+
+
+# XmlItem
+
+## Properties
+
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**attributeString** | **String** |  |  [optional]
+**attributeNumber** | [**BigDecimal**](BigDecimal.md) |  |  [optional]
+**attributeInteger** | **Integer** |  |  [optional]
+**attributeBoolean** | **Boolean** |  |  [optional]
+**wrappedArray** | **List<Integer>** |  |  [optional]
+**nameString** | **String** |  |  [optional]
+**nameNumber** | [**BigDecimal**](BigDecimal.md) |  |  [optional]
+**nameInteger** | **Integer** |  |  [optional]
+**nameBoolean** | **Boolean** |  |  [optional]
+**nameArray** | **List<Integer>** |  |  [optional]
+**nameWrappedArray** | **List<Integer>** |  |  [optional]
+**prefixString** | **String** |  |  [optional]
+**prefixNumber** | [**BigDecimal**](BigDecimal.md) |  |  [optional]
+**prefixInteger** | **Integer** |  |  [optional]
+**prefixBoolean** | **Boolean** |  |  [optional]
+**prefixArray** | **List<Integer>** |  |  [optional]
+**prefixWrappedArray** | **List<Integer>** |  |  [optional]
+**namespaceString** | **String** |  |  [optional]
+**namespaceNumber** | [**BigDecimal**](BigDecimal.md) |  |  [optional]
+**namespaceInteger** | **Integer** |  |  [optional]
+**namespaceBoolean** | **Boolean** |  |  [optional]
+**namespaceArray** | **List<Integer>** |  |  [optional]
+**namespaceWrappedArray** | **List<Integer>** |  |  [optional]
+**prefixNsString** | **String** |  |  [optional]
+**prefixNsNumber** | [**BigDecimal**](BigDecimal.md) |  |  [optional]
+**prefixNsInteger** | **Integer** |  |  [optional]
+**prefixNsBoolean** | **Boolean** |  |  [optional]
+**prefixNsArray** | **List<Integer>** |  |  [optional]
+**prefixNsWrappedArray** | **List<Integer>** |  |  [optional]
+
+
+