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/EnumTest.md

@@ -0,0 +1,54 @@
+
+
+# EnumTest
+
+## Properties
+
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**enumString** | [**EnumStringEnum**](#EnumStringEnum) |  |  [optional]
+**enumStringRequired** | [**EnumStringRequiredEnum**](#EnumStringRequiredEnum) |  | 
+**enumInteger** | [**EnumIntegerEnum**](#EnumIntegerEnum) |  |  [optional]
+**enumNumber** | [**EnumNumberEnum**](#EnumNumberEnum) |  |  [optional]
+**outerEnum** | [**OuterEnum**](OuterEnum.md) |  |  [optional]
+
+
+
+## Enum: EnumStringEnum
+
+Name | Value
+---- | -----
+UPPER | "UPPER"
+LOWER | "lower"
+EMPTY | ""
+
+
+
+## Enum: EnumStringRequiredEnum
+
+Name | Value
+---- | -----
+UPPER | "UPPER"
+LOWER | "lower"
+EMPTY | ""
+
+
+
+## Enum: EnumIntegerEnum
+
+Name | Value
+---- | -----
+NUMBER_1 | 1
+NUMBER_MINUS_1 | -1
+
+
+
+## Enum: EnumNumberEnum
+
+Name | Value
+---- | -----
+NUMBER_1_DOT_1 | 1.1
+NUMBER_MINUS_1_DOT_2 | -1.2
+
+
+