**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
"""Historical as_dict"""
    warnings.warn(
        "Accessing configuration method 'as_dict' directly from the configuration module is "
        "deprecated. Please access the configuration from the 'configuration.conf' object via "
        "'conf.as_dict'",
        DeprecationWarning,
        stacklevel=2,
    )
    return conf.as_dict(*args, **kwargs)
def set(*args, **kwargs):
    """Historical set"""
    warnings.warn(
        "Accessing configuration method 'set' directly from the configuration module is "
        "deprecated. Please access the configuration from the 'configuration.conf' object via "
        "'conf.set'",
        DeprecationWarning,
        stacklevel=2,
    )
    return conf.set(*args, **kwargs)
def ensure_secrets_loaded() -> List[BaseSecretsBackend]:
    """
    Ensure that all secrets backends are loaded.
    If the secrets_backend_list contains only 2 default backends, reload it.
    """
    
    if len(secrets_backend_list) == 2:
        return initialize_secrets_backends()
    return secrets_backend_list
def get_custom_secret_backend() -> Optional[BaseSecretsBackend]: