fix Added copy of HTTP_ROUTE to the metrics attribute

[lionskape]

Which problem is this PR solving?

There is no way to set http.route for metrics

Short description of the changes

Added copy from span of HTTP_ROUTE attribute. It is low cordiality attribute, which is very useful on metrics.

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[pichlermarc]

Thanks for reaching out, I think there may be a misunderstanding what this instrumentation does.

http.route is not a valid client metrics attribute according to the semantic conventions. It is only valid on server metrics. (see HTTP Semantic Conventions).

Also the span attributes don't contain http.route as this is a server attribute for Spans as well. The client woudn't know which route the server uses.

[pichlermarc]

http.route is not a client metrics attribute. see https://github.com/open-telemetry/semantic-conventions/blob/main/docs/http/http-metrics.md#metric-httpclientrequestduration

Also the attributes in this method don't contain http.route, so there's no point in copying them.

[lionskape]

For sure, I have added http.route using custom attribute mechanics to the span.

[lionskape]

@pichlermarc thank you. So, I will purpose an mechanic to add custom attributes for metrics in another PR.

It is very strange for me, that http.route is not applicable to client metrics. It is very common pattern to has low cardinality label on request metrics (to determine on "where does the request goes"). In my case - it is almost useless metric, without http.route.