[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/others/java/restclient-useAbstractionForFiles/api/openapi.yaml

@@ -0,0 +1,26 @@
+openapi: 3.0.1
+info:
+  title: Response file abstraction test
+  version: 1.0.0
+servers:
+- url: /
+paths:
+  /resource:
+    get:
+      description: Response file abstraction
+      operationId: resourceInResponse
+      responses:
+        "200":
+          content:
+            application/octet-stream:
+              schema:
+                format: binary
+                type: string
+          description: Successful operation
+      tags:
+      - resource
+      x-accepts:
+      - application/octet-stream
+components:
+  schemas: {}
+