Support for HttpApis?

I can see that according to the documentation, REST APIs can automatically propagate requests to their lambda handlers.

However, this isn't supported for HTTP APIs.

### Use case

We have a microservices setup where API A might call API B, and we want X-Ray to trace all the way through.

Right now we use a workaround where we parse the `x-amzn-trace-id` header and create a new segment for each invocation. This kind of works, but it loses the subsegments generated by the Lambda service (which can tell us about e.g. cold start times). It's also ugly because now we get a DAG in the service graph with duplicates, like

```
client --> lambda --> lambda function
-------------> lambda function
```

This same kind of issue gets propagated to downstream calls, messing up our service graph.

I guess that this would have to be solved at the api gateway level, telling api gateway to continue the trace, passing this along to the lambda service and finally the lambda function?

Any direction or information here would be helpful. Thanks!