Fix package init (#1572)

New formatter removed the imports without __all__.

Author: therve

src/datadog_api_client/__init__.py

@@ -1,3 +1,9 @@
 # Unless explicitly stated otherwise all files in this repository are licensed under the Apache-2.0 License.
 # This product includes software developed at Datadog (https://www.datadoghq.com/).
 # Copyright 2019-Present Datadog, Inc.
+
+from datadog_api_client.api_client import ApiClient, AsyncApiClient, ThreadedApiClient
+from datadog_api_client.configuration import Configuration
+
+
+__all__ = ["ApiClient", "AsyncApiClient", "ThreadedApiClient", "Configuration"]