Span lifespan

[Som-Som-CC]

At client tracing spans are to be started when the request is to be sent and closed when the response arrived (or whatever way the request is terminated). The current implementation, however, creates and then closes the span immediately.

The reason arises from the old tracing mechanism, which just dealt with propagation and did no reporting using OpenTelemetry. Now instead of a string for logging a real a span object is to be created within the Do function, with its own close mechanism.

[Som-Som-CC]

Since otelhttp.NewTransport transport is used at http.Client that does the instrumentation, we do not really need to care about span and its lifespan. So, this ticket is the other way around, no need in restful to create a new span when otel is used. A small code cleanup may be needed.

On the other hand, logging still uses span ID, so that requests and responses to be correlated. Other frameworks log request and response together. But that means that request logging is not in line with the other logs an app prints.