0.7.0: files and resources show up as "unrouted" in generated traces

[hlship]

The new telemetry support largely works well, but while experimenting, I found that trace data is missing for any response that is not generated due to routing; this include the resource and file interceptors, and perhaps others.

We should find a way for such interceptor to communicate (via a context key) that they generated a response, even if it wasn't routed, that can be used by the request tracing interceptor to generate a reasonable name for the trace.