Is your feature request related to a problem? Please describe

Services usually have a server span upon request entry and client span (span.kind = client) around calls to upstream.

This helps with a few things:

1. You can diagnose whether time is being spent or errors in the service itself or its upstreams.
2. Tracing products use this information for useful visualisations e.g. "inferred services" for services that haven't adopted tracing it still shows up as a dependency.

Describe the solution you'd like

1. Output a new span on each calls to upstream
2. Allow adding attributes/baggage only to that client span

Describe alternatives you've considered

Putting a proxy between nginx and its upstreams.