**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 section == deprecated_section:
            warnings.warn(
                'The {old} option in [{section}] has been renamed to {new} - the old '
                'setting has been used, but please update your config.'.format(
                    old=deprecated_name,
                    new=key,
                    section=section,
                ),
                DeprecationWarning,
                stacklevel=3,
            )
        else:
            warnings.warn(
                'The {old_key} option in [{old_section}] has been moved to the {new_key} option in '
                '[{new_section}] - the old setting has been used, but please update your config.'.format(
                    old_section=deprecated_section,
                    old_key=deprecated_name,
                    new_key=key,
                    new_section=section,
                ),
                DeprecationWarning,
                stacklevel=3,
            )
    def __getstate__(self):