Fix otelhttptrace example to avoid duplicating the generated data

[dmathieu]

Closes #5562

This example shows both ways to setup otelhttptrace, but WithClientTrace appends tracers, it does not replace them. So someone running the example gets duplicated data, which is confusing.

I have chosen to remove the example from the client, as that's our own option. Passing it to the context is "the httptrace way".

[zdyj3170101136]

Closes #5562

This example shows both ways to setup otelhttptrace, but WithClientTrace appends tracers, it does not replace them. So someone running the example gets duplicated data, which is confusing.

I have chosen to remove the example from the client, as that's our own option. Passing it to the context is "the httptrace way".

i recommend you reserve the first way.

first way:

Transport: otelhttp.NewTransport(
			http.DefaultTransport,
			otelhttp.WithClientTrace(func(ctx context.Context) *httptrace.ClientTrace {
				return otelhttptrace.NewClientTrace(ctx)
			}),
		),

second way:

req, _ := http.NewRequestWithContext(ctx, "GET", *url, nil)

the first way's jaeger ui is easier for user to understand.

and is much easier for user to use(it could just replace global http.Transport)

[dmathieu]

You're right, thank you.
When we add it to the context before the HTTP span is started, the used context doesn't have the proper span parent.