Add a trace-id tag to the k6 HTTP metric

[ppcano]

k6 stores various information as Tags for each metric data point.

For further investigation on the observability provider, it could be useful to add a tag with the trace-id value.

This feature could be included without the need for k6 changes. Mihail commented:

the http api takes Params as it's latest argument and you can add tags to it. But you need to be careful to add the additional tags to the last argument object as described in the js api docs instead of jsut to keep adding arguments aka
http.get(url, {headers: , tags: }) is correct http.get(url, {headers: }, {tags: }) doesn't work 🙂
Looking at the code this is likely a problem as well now as the current code just adds headers and if there is already something else provided as the last argument, the trace headers will just be added as another argument which will unfortunately not work 😉