[Python] add '_spec_property_naming' param

[JoeCqupt]

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (5.3.0), 6.0.x
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

[JoeCqupt]

call for view @spacether

[JoeCqupt]

when i use python-sdk (generated by OpenApi-Generator) invoking some api. i need set _spec_property_naming param is True. but now it always is False . so i modified the template files to make this param can pass by **kwargs

[spacether]

Why is this PR needed?
spec_property_naming is not always False.

• When models are input into endpoints, one can first instantiate them with python naming like Model(some_arg='blah')
• When models are input into endpoints, one can first instantiate them with spec property naming like Model(someArg='blah', _spec_property_naming=True) see this example here
• When a payload is returned from a server and is deserialized, spec_property naming is set to True here: https://github.com/OpenAPITools/openapi-generator/blob/master/samples/openapi3/client/petstore/python/petstore_api/api_client.py#L329 which invokes Model._new_from_openapi_data(someArg='blah, _spec_property_naming=True)

[JoeCqupt]

use case:
we use openapi-generator-cli generate a python-sdk . but we can not confirm is this sdk work right ?

so we make a sdk-tester service. this service imitate an api-service. it accept json data and use python reflectiton to invoke sdk method to call remote real api-service. in this way. we can simply to test sdk

because i use json data(it is dict) to invoke sdk method . so the property name of model is not match.
our json data variable name follow camel case. the variable name of model follow snake case.
this will cause method validate_and_convert_types throw exception

[spacether]

CI failure is unrelated

[spacether]

Thank you for your PR; this looks good!