[BUG][Python] Bug generating invalid Configuration class with missing access_token

Created by: zilvinasu

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?
[Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

I am generating Python client for my OpenAPI and it is outputting invalid Python code, where it has a Configuration class, which is trying to use self.access_token which is not initialised to any default value.

openapi-generator version

v.4.2.0

OpenAPI declaration file content or url

Generation Details

docker run --rm \
		-v "${PWD}:/repo" openapitools/openapi-generator-cli generate \
		-i /repo/spec.yaml \
		-g python --package-name "my_api" \
		-o /repo/openapi/my_api

Steps to reproduce

With generated client, just go to configuration.py you will see that self.access_token is being used, though it was not initialised anywhere.

Suggest a fix

Initialise access_token value to None by default