Load Django environment from config file

CONFIG_INI = Path(os.environ.get('DJANGO_CONFIG_INI', BASE_DIR / 'config.ini'))
if CONFIG_INI.exists():
    config = RawConfigParser()
    config.read_file(CONFIG_INI.open())
    if not config.has_section('django'):
        raise ImproperlyConfigured('Missing `django` section in environment file: %s', CONFIG_INI)
    for k,v in config.items('django'):
        e = k.upper()
        if e not in os.environ: # Don't overwrite existing
            os.environ[e] = v