**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
"""Get Config option values from Secret Backend"""
        fallback_key = key + '_secret'
        
        if (section, key) in self.sensitive_config_values:
            if super().has_option(section, fallback_key):
                secrets_path = super().get(section, fallback_key)
                return _get_config_value_from_secret_backend(secrets_path)
        return None
    def get(self, section, key, **kwargs):
        section = str(section).lower()
        key = str(key).lower()
        deprecated_section, deprecated_key, _ = self.deprecated_options.get(
            (section, key), (None, None, None)
        )
        option = self._get_environment_variables(deprecated_key, deprecated_section, key, section)
        if option is not None:
            return option
        option = self._get_option_from_config_file(deprecated_key, deprecated_section, key, kwargs, section)
        if option is not None:
            return option
        option = self._get_option_from_commands(deprecated_key, deprecated_section, key, section)
        if option is not None:
            return option
        option = self._get_option_from_secrets(deprecated_key, deprecated_section, key, section)
        if option is not None:
            return option
        return self._get_option_from_default_config(section, key, **kwargs)
    def _get_option_from_default_config(self, section, key, **kwargs):