**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
"""Custom Airflow Configparser supporting defaults and deprecated options"""
    
    
    
    
    
    sensitive_config_values = {
        ('core', 'sql_alchemy_conn'),
        ('core', 'fernet_key'),
        ('celery', 'broker_url'),
        ('celery', 'flower_basic_auth'),
        ('celery', 'result_backend'),
        ('atlas', 'password'),
        ('smtp', 'smtp_password'),
        ('webserver', 'secret_key'),
    }
    
    
    
    deprecated_options = {
        ('celery', 'worker_precheck'): ('core', 'worker_precheck', '2.0.0'),
        ('logging', 'base_log_folder'): ('core', 'base_log_folder', '2.0.0'),
        ('logging', 'remote_logging'): ('core', 'remote_logging', '2.0.0'),
        ('logging', 'remote_log_conn_id'): ('core', 'remote_log_conn_id', '2.0.0'),
        ('logging', 'remote_base_log_folder'): ('core', 'remote_base_log_folder', '2.0.0'),
        ('logging', 'encrypt_s3_logs'): ('core', 'encrypt_s3_logs', '2.0.0'),
        ('logging', 'logging_level'): ('core', 'logging_level', '2.0.0'),
        ('logging', 'fab_logging_level'): ('core', 'fab_logging_level', '2.0.0'),
        ('logging', 'logging_config_class'): ('core', 'logging_config_class', '2.0.0'),