[Java][Client] Add support for the new Spring RestClient (#18522)

* feat (JAVA SPRING RESTTEMPLATE) 17571: initial commit for Spring RestClient

* feat (JAVA SPRING RESTTEMPLATE) 17571: Copied and changed the webclient mustache files

The RestClient API is oriented on the WebClient API so many parts of the templates can be the same

* fix (JAVA SPRING RESTTEMPLATE) 17571: Renaming error & add README template

The README must be changed because the minimal Java Version for this client is 17

* fix (JAVA SPRING RESTTEMPLATE) 17571: Imports, compile errors and cookie setting

* feat (JAVA SPRING RESTTEMPLATE) 17571: Add generated samples

* test (JAVA SPRING RESTTEMPLATE) 17571: Add tests

* feat (JAVA SPRING RESTTEMPLATE) 17571: Update doc

* Add the restcilent to samples-java-client-jdk17.yam

The minimum Java version of the used Spring Version is 17

* fix (JAVA SPRING RESTTEMPLATE) 17571: Workflow paths to petstore samples

* fix (JAVA SPRING RESTTEMPLATE) 17571: Regenerated samples

* feat (JAVA SPRING RESTTEMPLATE) 17571: Generated echo-api sample for RestClient

* fix (JAVA SPRING RESTTEMPLATE) 17571: Missing import

* fix (JAVA SPRING RESTTEMPLATE) 17571: Missing body class exception when null body is set

* test (JAVA SPRING RESTTEMPLATE) 17571: Add echo-api Auth test

* fix (JAVA SPRING RESTTEMPLATE) 17571: Gradlew file permissions

* feat (JAVA SPRING RESTTEMPLATE) 17571: Reggenerate samples after rebase

* test (JAVA SPRING RESTTEMPLATE) 17571: Add echo-api Body gif test

* test (JAVA SPRING RESTTEMPLATE) 17571: Add echo-api octet stream body test

* test (JAVA SPRING RESTTEMPLATE) 17571: Add echo-api multipart form data test

* fix (JAVA SPRING RESTTEMPLATE) 17571: Form as body when body is null

Also regenerated the restclient samples

samples/client/echo_api/java/restclient/docs/Pet.md

@@ -0,0 +1,28 @@
+
+
+# Pet
+
+
+## Properties
+
+| Name | Type | Description | Notes |
+|------------ | ------------- | ------------- | -------------|
+|**id** | **Long** |  |  [optional] |
+|**name** | **String** |  |  |
+|**category** | [**Category**](Category.md) |  |  [optional] |
+|**photoUrls** | **List<String>** |  |  |
+|**tags** | [**List<Tag>**](Tag.md) |  |  [optional] |
+|**status** | [**StatusEnum**](#StatusEnum) | pet status in the store |  [optional] |
+
+
+
+## Enum: StatusEnum
+
+| Name | Value |
+|---- | -----|
+| AVAILABLE | "available" |
+| PENDING | "pending" |
+| SOLD | "sold" |
+
+
+