Add option to customize span name

[RangelReale]

This PR adds an option to customize span name.

	hook := newTracingHook(
		"",
		WithTracerProvider(provider),
		WithSpanName(func(hook TracingHook, defaultName string) string {
			if hook == TracingHookProcess {
				return "redis." + defaultName
			}
			return defaultName
		}),
	)

[chayim]

@RangelReale What's your use case?

[RangelReale]

@RangelReale What's your use case?

It's mostly because in Datadog when you are looking at the latest traces, the only thing shown is the span name. So I see "GET <url>" for http, "db.query", "db.tx" for sql, but for redis I see just "get", "put", I wanted to at least show "redis.get" and "redis.put", to at least know what it is for.

[ndyakov]

Closing for inactivity, feel free to reopen when synced with master.

[RangelReale]

Synced with master.

[RangelReale]

Can't see to find a way to reopen.