[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/StringEnumRef.md

@@ -0,0 +1,15 @@
+
+
+# StringEnumRef
+
+## Enum
+
+
+* `SUCCESS` (value: `"success"`)
+
+* `FAILURE` (value: `"failure"`)
+
+* `UNCLASSIFIED` (value: `"unclassified"`)
+
+
+