[Java] Templates to support google-api-client library (#6838)

* Add support for the google-api-client

* When there's no return type, just return (no parsing the response)

* Update the deserialization to use a Jackson typeref.

* Delete the auth mustache files as we don't need them

* Stop generating unneeded auth files; get SBT/gradle working with the generated module

* Add builder-style methods to the google-api-client ApiClient for getting API instances

* Update the README to reflect the new client library option

* Generated overloaded methods to send query params as a Map<String, Object>

* Add files for Sample codes

* Add type in angle brackets to support Java 6

* Required query params must be added to the Map of params. Update sample code.

* Use explicit types instead of diamonds to support Java6 in one more place.

* Clean up javadoc warnings in generated code / remove pointless return statements

* Clean up extra newlines in generated code

samples/client/petstore/java/google-api-client/docs/EnumArrays.md

@@ -0,0 +1,27 @@
+
+# EnumArrays
+
+## Properties
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**justSymbol** | [**JustSymbolEnum**](#JustSymbolEnum) |  |  [optional]
+**arrayEnum** | [**List<ArrayEnumEnum>**](#List<ArrayEnumEnum>) |  |  [optional]
+
+
+<a name="JustSymbolEnum"></a>
+## Enum: JustSymbolEnum
+Name | Value
+---- | -----
+GREATER_THAN_OR_EQUAL_TO | &quot;&gt;&#x3D;&quot;
+DOLLAR | &quot;$&quot;
+
+
+<a name="List<ArrayEnumEnum>"></a>
+## Enum: List&lt;ArrayEnumEnum&gt;
+Name | Value
+---- | -----
+FISH | &quot;fish&quot;
+CRAB | &quot;crab&quot;
+
+
+