**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
"""
        Remove an option if it exists in config from a file or
        default config. If both of config have the same option, this removes
        the option in both configs unless remove_default=False.
        """
        if super().has_option(section, option):
            super().remove_option(section, option)
        if self.airflow_defaults.has_option(section, option) and remove_default:
            self.airflow_defaults.remove_option(section, option)
    def getsection(self, section: str) -> Optional[Dict[str, Union[str, int, float, bool]]]:
        """
        Returns the section as a dict. Values are converted to int, float, bool
        as required.
        :param section: section from the config
        :rtype: dict
        """
        if not self.has_section(section) and not self.airflow_defaults.has_section(section):
            return None
        if self.airflow_defaults.has_section(section):
            _section = OrderedDict(self.airflow_defaults.items(section))
        else:
            _section = OrderedDict()
        if self.has_section(section):
            _section.update(OrderedDict(self.items(section)))
        section_prefix = self._env_var_name(section, '')
        for env_var in sorted(os.environ.keys()):
            if env_var.startswith(section_prefix):