**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
self,
        display_source=False,
        display_sensitive=False,
        raw=False,
        include_env=True,
        include_cmds=True,
        include_secret=True,
    ) -> Dict[str, Dict[str, str]]:
        """
        Returns the current configuration as an OrderedDict of OrderedDicts.
        :param display_source: If False, the option value is returned. If True,
            a tuple of (option_value, source) is returned. Source is either
            'airflow.cfg', 'default', 'env var', or 'cmd'.
        :type display_source: bool
        :param display_sensitive: If True, the values of options set by env
            vars and bash commands will be displayed. If False, those options
            are shown as '< hidden >'
        :type display_sensitive: bool
        :param raw: Should the values be output as interpolated values, or the
            "raw" form that can be fed back in to ConfigParser
        :type raw: bool
        :param include_env: Should the value of configuration from AIRFLOW__
            environment variables be included or not