Warnar Boekkooi

@dmathieu I tried that first but that makes the if statements (in [wroteHeaders](https://github.com/open-telemetry/opentelemetry-go-contrib/blob/main/instrumentation/net/http/httptrace/otelhttptrace/clienttrace.go#L345) and [wroteHeaderField](https://github.com/open-telemetry/opentelemetry-go-contrib/blob/main/instrumentation/net/http/httptrace/otelhttptrace/clienttrace.go#L330)) that currently check for `nil` harder, so I went for sticking to the existing method...

@pellared Sorry I had to rebase (and I squashed the changes as coffee detox made me fetch the wrong remote :see_no_evil:)

Thanks @pellared and @dmathieu for reviewing and sorry for the back and forth on this one.

Hello @roidelapluie, @gotjosh, @ArthurSens, Would one of you maybe have time to review this PR? Thanks in advance and have a great day!

Hi @rueian Thanks a lot for the fast retry and all the info! I agree that using the clients `OnInvalidations` is preferred but it is a bit limiting for my...