Improved resource naming for HTTP client requests

[morley92]

We're sending OTEL HTTP client spans via the DataDog agent.

Trace metrics are successfully mapped from these HTTP client spans as you would expect e.g. trace.client.hits.by_http_status. These have some standard attributes included such as http.status_code etc.

The resource_name attribute of the trace metric however is simply the HTTP request method e.g. GET. This is not very useful for aggregating such trace metrics by the request path - which is a common use of such metrics.

Looking through the source, it appears that the resource_name is calculated based on a combination of http.request.method and http.route. If http.route is not found then it will simply use http.request.method - which is the behaviour we're seeing.

The semantic guidelines for HTTP client spans using OTEL don't specify http.route as a valid attribute - this is actually intended for HTTP server spans. url.full is the closest stable attribute as far as I can tell.

Is this a bug or intentional?