* and stop setting default values in python operator code, so defaults can be set at the server side.

This issue is just for the PR and questions from maintainers. 
setup.py
When installing providers from sources we install all namespace packages found below airflow,
        including airflow and provider packages, otherwise defaults from setup.cfg control this.
        The kwargs in setup() call override those that are specified in setup.cfg.
        """
        if os.getenv(INSTALL_PROVIDERS_FROM_SOURCES) == 'true':
            setup_kwargs['packages'] = find_namespace_packages(include=['airflow*'])
    include_provider_namespace_packages_when_installing_from_sources()
    if os.getenv(INSTALL_PROVIDERS_FROM_SOURCES) == 'true':
        print("Installing providers from sources. Skip adding providers as dependencies")
    else:
        add_all_provider_packages()
    write_version()
    setup(
        distclass=AirflowDistribution,
        version=version,
        extras_require=EXTRAS_REQUIREMENTS,
        download_url=('https://archive.apache.org/dist/airflow/' + version),
        cmdclass={
            'extra_clean': CleanCommand,
            'compile_assets': CompileAssets,
            'list_extras': ListExtras,
            'install': Install,
            'develop': Develop,
        },
        test_suite='setup.airflow_test_suite',
        **setup_kwargs,
    )
if __name__ == "__main__":
    do_setup()