[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/AnotherFakeApi.md

@@ -0,0 +1,54 @@
+# AnotherFakeApi
+
+All URIs are relative to *http://petstore.swagger.io:80/v2*
+
+Method | HTTP request | Description
+------------- | ------------- | -------------
+[**testSpecialTags**](AnotherFakeApi.md#testSpecialTags) | **PATCH** /another-fake/dummy | To test special tags
+
+
+<a name="testSpecialTags"></a>
+# **testSpecialTags**
+> Client testSpecialTags(body)
+
+To test special tags
+
+To test special tags
+
+### Example
+```java
+// Import classes:
+//import io.swagger.client.ApiException;
+//import io.swagger.client.api.AnotherFakeApi;
+
+
+AnotherFakeApi apiInstance = new AnotherFakeApi();
+Client body = new Client(); // Client | client model
+try {
+    Client result = apiInstance.testSpecialTags(body);
+    System.out.println(result);
+} catch (ApiException e) {
+    System.err.println("Exception when calling AnotherFakeApi#testSpecialTags");
+    e.printStackTrace();
+}
+```
+
+### Parameters
+
+Name | Type | Description  | Notes
+------------- | ------------- | ------------- | -------------
+ **body** | [**Client**](Client.md)| client model |
+
+### Return type
+
+[**Client**](Client.md)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+ - **Content-Type**: application/json
+ - **Accept**: application/json
+