Tracing for non-HTTP routers

[sofixa]

Do you want to request a feature or report a bug?

Feature ( the lack thereof, or at least the lack of clarity around it in the docs could be considered kind of a bug)

What did you expect to see?

Jaeger does tracing as per its docs. However, nowhere in the docs does it say that that it doesn't do tracing on non-HTTP routers ( TCP and UDP), which seems to be the case based on the code, for instance :

https://github.com/traefik/traefik/blob/ac486d3d1df7a788a60f6c2f9962c2bac073b1b0/pkg/tracing/tracing.go#L75-L80

Everything works on r *http.Request.

Ideally i'd like to see tracing for TCP and UDP routers as well as HTTP, but at the very least a mention needs to be added to the docs that only HTTP routers get tracing.

PS: There's #7669 , which was closed due to old age.