http headers are canonicalized before sending

[agilob]

Despite the header being specified in lower case https://github.com/grafana/xk6-distributed-tracing/blob/master/client/traceid.go#L16

when it's put to a map golang changes the key to a canonicalized version which always starts with Uppercase letter this breaks compatibility of the b3 spec. Request aren't picked up by existing b3-compatible backends.

The expected header is b3, but remote backend receives B3, span and parent trace id aren't picked up:

[Blinkuu]

Archiving this repository, as k6/experimental/tracing module is now available in k6 OSS.