[Kotlin][Client] Added supporting Retrofit2(RxJava/RxJava2/Coroutines) (#5750)

* Added support Retrofit2(RxJava/RxJava2/Coroutines) to Kotlin client code generator

* Added generated samples for Retrofit2(RxJava/RxJava2/Coroutines) on Kotlin

* Fixed generating retrofit2 without Rx/Coroutines

* Fixed MultipartBody template, remove redundant space after MultipartBody.Part annotation

* Fix documentation diff.

* Fix generating build.gradle file for samples.
Add dependencies for rxJava/rxJava2 and rx retrofit's adapter.

* Update generated sample with rx dependencies

* Update generated sample with coroutines

* Update generated sample with RxJava 2 dependencies

* Update and refactoring scripts for sample generation

* Update generated sample code

* revert changes by mistake

* revert changes by mistake #2

* Fix return type for first RxJava

* Add RxJavaCallAdapterFactory to ApiClient scheme for RxJava 1/2

* Fix script loggin

* Update generated code for RxJava 1/2

* Fix kotlin.md documentation by script export_docs_generators.sh

* Update Kotlin samples project in pom.xml

* Revert "Update Kotlin samples project in pom.xml"

This reverts commit 9de4d0ba

* Fixed "" wrapping number types for annotation value
Fixed generating polymorphic interfaces for Gson, interface fields can't be marked with @SerializedName annotation, it's enough to mark it in child model.
Fixed instantiationTypes(array, list, map) for Kotlin generator

* Update Kotlin samples project after last fixes

* Update Kotlin samples project for kotlin-jvm-*

* Update Kotlin readme.md documentations

* Update Kotlin client sample changes

* Fixed encoding braces for generics model

* Update Kotlin client sample changes

* Update Kotlin client sample after merge with master

* Fixed adding empty braces for inherit from Map/Array

* Update sample model after last fix with empty braces

* Revert adding @SerializedName to Kotlin interface fields through @get:SerializedName as for Jackson

* Update Kotlin client samples with adding @get:SerializedName

samples/openapi3/client/petstore/kotlin/docs/FakeApi.md

@@ -5,6 +5,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 Method | HTTP request | Description
 ------------- | ------------- | -------------
 [**fakeHealthGet**](FakeApi.md#fakeHealthGet) | **GET** /fake/health | Health check endpoint
+[**fakeHttpSignatureTest**](FakeApi.md#fakeHttpSignatureTest) | **GET** /fake/http-signature-test | test http signature authentication
 [**fakeOuterBooleanSerialize**](FakeApi.md#fakeOuterBooleanSerialize) | **POST** /fake/outer/boolean | 
 [**fakeOuterCompositeSerialize**](FakeApi.md#fakeOuterCompositeSerialize) | **POST** /fake/outer/composite | 
 [**fakeOuterNumberSerialize**](FakeApi.md#fakeOuterNumberSerialize) | **POST** /fake/outer/number | 
@@ -61,6 +62,54 @@ No authorization required
  - **Content-Type**: Not defined
  - **Accept**: application/json
 
+<a name="fakeHttpSignatureTest"></a>
+# **fakeHttpSignatureTest**
+> fakeHttpSignatureTest(pet, query1, header1)
+
+test http signature authentication
+
+### Example
+```kotlin
+// Import classes:
+//import org.openapitools.client.infrastructure.*
+//import org.openapitools.client.models.*
+
+val apiInstance = FakeApi()
+val pet : Pet =  // Pet | Pet object that needs to be added to the store
+val query1 : kotlin.String = query1_example // kotlin.String | query parameter
+val header1 : kotlin.String = header1_example // kotlin.String | header parameter
+try {
+    apiInstance.fakeHttpSignatureTest(pet, query1, header1)
+} catch (e: ClientException) {
+    println("4xx response calling FakeApi#fakeHttpSignatureTest")
+    e.printStackTrace()
+} catch (e: ServerException) {
+    println("5xx response calling FakeApi#fakeHttpSignatureTest")
+    e.printStackTrace()
+}
+```
+
+### Parameters
+
+Name | Type | Description  | Notes
+------------- | ------------- | ------------- | -------------
+ **pet** | [**Pet**](Pet.md)| Pet object that needs to be added to the store |
+ **query1** | **kotlin.String**| query parameter | [optional]
+ **header1** | **kotlin.String**| header parameter | [optional]
+
+### Return type
+
+null (empty response body)
+
+### Authorization
+
+
+
+### HTTP request headers
+
+ - **Content-Type**: application/json, application/xml
+ - **Accept**: Not defined
+
 <a name="fakeOuterBooleanSerialize"></a>
 # **fakeOuterBooleanSerialize**
 > kotlin.Boolean fakeOuterBooleanSerialize(body)
@@ -414,7 +463,7 @@ val float : kotlin.Float = 3.4 // kotlin.Float | None
 val string : kotlin.String = string_example // kotlin.String | None
 val binary : java.io.File = BINARY_DATA_HERE // java.io.File | None
 val date : java.time.LocalDate = 2013-10-20 // java.time.LocalDate | None
-val dateTime : java.time.LocalDateTime = 2013-10-20T19:20:30+01:00 // java.time.LocalDateTime | None
+val dateTime : java.time.OffsetDateTime = 2013-10-20T19:20:30+01:00 // java.time.OffsetDateTime | None
 val password : kotlin.String = password_example // kotlin.String | None
 val paramCallback : kotlin.String = paramCallback_example // kotlin.String | None
 try {
@@ -443,7 +492,7 @@ Name | Type | Description  | Notes
  **string** | **kotlin.String**| None | [optional]
  **binary** | **java.io.File**| None | [optional]
  **date** | **java.time.LocalDate**| None | [optional]
- **dateTime** | **java.time.LocalDateTime**| None | [optional]
+ **dateTime** | **java.time.OffsetDateTime**| None | [optional]
  **password** | **kotlin.String**| None | [optional]
  **paramCallback** | **kotlin.String**| None | [optional]