Introduces a helper function within tvix-tracing that returns a reqwest
tracing middleware that will ingest the traceparent if otlp is enabled.
It is feature flagged in tvix-tracing so not every consumer of that
library automatically has reqwest in its dependencies.
Tested using netcat to verify that the `traceparent` header is there if
otlp is enabled and missing if otlp feature is disabled.
Change-Id: I5abccae777b725f5ff7382e3686165383c477a39
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11886
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
618aacaa61