**Description**

Enabled list of cors headers origin allowed

**Use case / motivation**

I'm currently developping Django application working with apache airflow for some external work through api. From Django, user run dag and a js request wait for dag end. By this way, I enabled cors headers in airflow.cfg with correct url. But now, I've  environment (dev & prod). It could be useful to be able to set more than one url in airflow.cfg cors header origin allowed

Thank's in advance :) 

airflow/configuration.py
return {
            name: getattr(self, name)
            for name in [
                '_sections',
                'is_validated',
                'airflow_defaults',
            ]
        }
    def __setstate__(self, state):
        self.__init__()
        config = state.pop('_sections')
        self.read_dict(config)
        self.__dict__.update(state)
def get_airflow_home():
    """Get path to Airflow Home"""
    return expand_env_var(os.environ.get('AIRFLOW_HOME', '~/airflow'))
def get_airflow_config(airflow_home):