add in_subsegment_async in dd

Author: roger-zhangg

aws_lambda_powertools/tracing/provider/datadog/dd_tracer.py

@@ -68,6 +68,8 @@ async def trace_async(
         ) as dd_span:
             yield DDSpan(dd_span=dd_span)
 
+    in_subsegment_async = trace_async
+
     def set_attribute(self, key: str | bytes, value: Any, **kwargs: Any) -> None:
         span = self.dd_tracer.context_provider.active()
         # ignore if no active span