Ktor: make `spanNameExtractor` configurable

[SIMULATAN]

Whilst the semconv doesn't explicitly require the URL to be part of the span name, I would like to see more information than just the request method there.

Thus, I propose to add a simple setSpanNameExtractor method to the AbstractKtorClientTracingBuilder, similar to what #8255 did. Something like this would do just fine:

fun setSpanNameExtractor(spanNameExtractor: SpanNameExtractor<in HttpRequestData>) {
	clientBuilder.setSpanNameExtractor { spanNameExtractor }
}

#9607 already brought this topic up, but the semconv has changed since then to include the url.template if enabled. In my opinion, my proposal would allow users to implement this, should they choose to, whilst preserving the original, non-experimental default.

[trask]

we would definitely accept a hook similar to what OkHttpTelemetryBuilder already has:

opentelemetry-java-instrumentation/instrumentation/okhttp/okhttp-3.0/library/src/main/java/io/opentelemetry/instrumentation/okhttp/v3_0/OkHttpTelemetryBuilder.java

Lines 97 to 106 in c2c5d80

	/** Sets custom {@link SpanNameExtractor} via transform function. */
	@CanIgnoreReturnValue
	public OkHttpTelemetryBuilder setSpanNameExtractor(
	Function<
	SpanNameExtractor<? super Interceptor.Chain>,
	? extends SpanNameExtractor<? super Interceptor.Chain>>
	spanNameExtractorTransformer) {
	builder.setSpanNameExtractor(spanNameExtractorTransformer);
	return this;
	}

[laurit]

Resolved with #12850