More descriptive operation names

[zdicesare]

Currently the span names are set to the method of the request, e.g. POST.

It would be helpful if this were something like: 'HTTP POST api/v1/foo/'
or just included the endpoint.

Alternatively, we could configure the tracer with a function that returns a span name from a request.

[pavolloffay]

Http verb as operation name is chosen on purpose. Path cannot be used as operation name because one endpoint /user/{id} can produce different operation names.