[BUG] [python] Endpoint required enums of length one unset

Created by: spacether

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

For required enums of length one, the python-experimental generator should be setting the default value to what the spec defines. We were previously doing this but a PR update accidentally wiped out this feature.

Endpoint parameter example Spec https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/test/resources/2_0/python-client-experimental/petstore-with-fake-endpoints-models-for-testing.yaml#L1066 Generated code https://github.com/OpenAPITools/openapi-generator/blob/master/samples/client/petstore/python-experimental/petstore_api/api/fake_api.py#L1016 I am not seeing a test of this, it looks like we are not correctly loading these default values into the function definition

openapi-generator version

master branch

OpenAPI declaration file content or url

Command line used for generation

Steps to reproduce

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/test/resources/2_0/python-client-experimental/petstore-with-fake-endpoints-models-for-testing.yaml#L1066

Suggest a fix

Please update the template here: https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/python/python-experimental/api.mustache#L48

• for required params with defaultValues, use the value
• switch to using the {{requiredVars}} and {{optional}} parameter tags and **kwargs like the model template does here https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/python/python-experimental/model_templates/method_init_shared.mustache#L1
• remove the sortParamsByRequiredFlag CLI option because this generator is hard coding us to
  • passing required params positionally in the function signature
  • add an endpoint test to ensure that this feature is tested

A dev user can:

• passing required params positionally OR
• passing required params as **kwargs (this is a general python feature where positional args can be passed as keyword args)