[BUG] isRestful flags are always returning false

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

When generating a new client from a valid OpenAPI 3 spec, the isRestful, isRestfulCreate, isRestfulShow, isRestfulUpdate, etc.. flags are always false in Mustache template. I have tried with several generators and seem to have the same issue with each one I tried. We need to modify the templates based on if the request is a GET, or a PUT/POST and it looks like since the templates are logicless, the only way to do that is to use the boolean isRestful flags. Please let me know if I am misunderstanding these flags or if there is a workaround to my issue.

openapi-generator version

4.3.1, 5.0.0beta1, 5.0.0beta2 all installed with npm install -g

OpenAPI declaration file content or url

https://github.com/OAI/OpenAPI-Specification/blob/master/examples/v3.0/petstore.yaml

Steps to reproduce

Run openapi-generator generate -i https://raw.githubusercontent.com/OAI/OpenAPI-Specification/master/examples/v3.0/petstore.yaml -g ruby --global-property=debugOperations and you will see that all endpoints/requests are set to "isRestful" : false even though they seem like they should all be true and that the POST request should be "isRestfulCreate" : true and GET should be `isRestful

Suggest a fix

I would expect all get, post, put, delete endpoints to set the isRestful flag as well as their more specific isRestfulCreate, isRestfulUpdate, etc... flag

Start by running the documented openapi-generator command against the OpenAPI petstore.yaml example with --global-property=debugOperations and inspect the generated operation flags. Trace how isRestful and the method-specific flags are populated for Mustache templates; done means GET, POST, PUT, and DELETE operations report the corresponding general and specific flags correctly.