Exporting NoopTracer publicly

[paulius-valiunas]

Some libraries (looking at you, Azure) annoyingly try to automatically enable tracing if they can require("@opentelemetry/api") from your dependency tree. Some of that tracing is too verbose for me as I don't want to have that many spans in my traces. I was looking for ways to disable tracing for this kind of libraries and the only feasible way that I found was creating a custom TracerProvider that looks at the library name passed into getTracer and either returns a NoopTracer or the usual SDK tracer based on a whitelist/blacklist of tracer names. The problem with that is NoopTracer is not included in the barrel file so I have to import it from @opentelemetry/api/build/src/trace/NoopTracer.js, which I understand might change at any time because it's not supposed to be used this way. I'm proposing that this is changed and people are allowed to import it directly.

[Flarna]

I think a custom sampler would be a better fit here.

But unfortunatelly samplers don't get the instrumentation scope info...

The spec mentions which parameters are required input for samplers but I don't read the more input is not allowed therefore I think adding instrumentation scope should be ok.

Or maybe you can decide based on span name and/or attributes given at span start already now - even this looks more like a workaround.