Upstream request statistics by path

*Description*:
Continuing the discussion on https://github.com/envoyproxy/envoy/issues/1585, it would be nice to have path tags on the `envoy.upstream_rq` for example.

In my opinion it should not be the actual path of the current request, as this could expose sensitive information and also make a lot of unnecessary dimensions on the metric.

But rather, having it based on the [RouteMatcher](https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/route/v3/route_components.proto#envoy-v3-api-msg-config-route-v3-routematch), specifically on `prefix`, `path` and `safe_regex`.

In the end, it does not really matter the full path being used at the moment, but rather which Envoy route was used, and the RouteMatcher would provide us a static and safe tag to be used.

*Another approach*:

Maybe another thing that could be done is by attaching a tag statically to a route and make that as a tag?
Maybe this exists somehow and I'm not aware? Like adding a tag from the route metadata for example...