**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/www/extensions/init_views.py
"""Initialize Experimental API"""
    if not conf.getboolean('api', 'enable_experimental_api', fallback=False):
        return
    from airflow.www.api.experimental import endpoints
    warnings.warn(
        "The experimental REST API is deprecated. Please migrate to the stable REST API. "
        "Please note that the experimental API do not have access control. "
        "The authenticated user has full access.",
        DeprecationWarning,
    )
    app.register_blueprint(endpoints.api_experimental, url_prefix='/api/experimental')
    app.extensions['csrf'].exempt(endpoints.api_experimental)