**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
#
#
import logging
import warnings
from os import path
from flask import Flask, request
from airflow._vendor import connexion
from airflow._vendor.connexion import ProblemException
from airflow.api_connexion.exceptions import common_error_handler
from airflow.configuration import conf
from airflow.security import permissions
from airflow.www.views import lazy_add_provider_discovered_options_to_connection_form
log = logging.getLogger(__name__)
ROOT_APP_DIR = path.abspath(path.join(path.dirname(__file__), path.pardir, path.pardir))
def init_flash_views(app):