**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
if self.airflow_defaults.has_option(section, key) or 'fallback' in kwargs:
            return expand_env_var(self.airflow_defaults.get(section, key, **kwargs))
        else:
            log.warning("section/key [%s/%s] not found in config", section, key)
            raise AirflowConfigException(f"section/key [{section}/{key}] not found in config")
    def _get_option_from_secrets(self, deprecated_key, deprecated_section, key, section):
        
        option = self._get_secret_option(section, key)
        if option:
            return option
        if deprecated_section:
            option = self._get_secret_option(deprecated_section, deprecated_key)
            if option:
                self._warn_deprecate(section, key, deprecated_section, deprecated_key)
                return option
        return None
    def _get_option_from_commands(self, deprecated_key, deprecated_section, key, section):