**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
"""
    Load the Airflow config files.
    Called for you automatically as part of the Airflow boot process.
    """
    global FERNET_KEY, AIRFLOW_HOME
    default_config = _parameterized_config_from_template('default_airflow.cfg')
    conf = AirflowConfigParser(default_config=default_config)
    if conf.getboolean('core', 'unit_test_mode'):
        
        if not os.path.isfile(TEST_CONFIG_FILE):
            from cryptography.fernet import Fernet
            log.info('Creating new Airflow config file for unit tests in: %s', TEST_CONFIG_FILE)
            pathlib.Path(AIRFLOW_HOME).mkdir(parents=True, exist_ok=True)
            FERNET_KEY = Fernet.generate_key().decode()
            with open(TEST_CONFIG_FILE, 'w') as file:
                cfg = _parameterized_config_from_template('default_test.cfg')
                file.write(cfg)
        conf.load_test_config()
    else:
        
        if not os.path.isfile(AIRFLOW_CONFIG):
            from cryptography.fernet import Fernet
            log.info('Creating new Airflow config file in: %s', AIRFLOW_CONFIG)
            pathlib.Path(AIRFLOW_HOME).mkdir(parents=True, exist_ok=True)
            FERNET_KEY = Fernet.generate_key().decode()
            with open(AIRFLOW_CONFIG, 'w') as file:
                file.write(default_config)
        log.info("Reading the config from %s", AIRFLOW_CONFIG)
        conf.read(AIRFLOW_CONFIG)
        if conf.has_option('core', 'AIRFLOW_HOME'):