update cpp-restsdk to use 3.0 petstore spec (#18670)

Author: wing328

bin/configs/cpp-restsdk-client.yaml

@@ -1,6 +1,6 @@
 generatorName: cpp-restsdk
 outputDir: samples/client/petstore/cpp-restsdk/client
-inputSpec: modules/openapi-generator/src/test/resources/2_0/petstore.yaml
+inputSpec: modules/openapi-generator/src/test/resources/3_0/cpp-restsdk/petstore.yaml
 templateDir: modules/openapi-generator/src/main/resources/cpp-rest-sdk-client
 additionalProperties:
   packageName: CppRestPetstoreClient