Simplify initialization

[dyladan]

Now that we introduced global context and propagation APIs, the user is required to initialize the tracer provider, the context manager, and the propagator before they can begin tracing. We should simplify this process with sane platform-specific defaults in some simple way. Possibly we should export some function from web and node packages like initializeGlobalDefaults or something?

[dyladan]

I asked in the spec SIG meeting how much freedom we have to do this, and the answer was that we can do basically whatever we deem appropriate as long as we don't violate spec or API. With that in mind, I think we should export some helper function from node and web packages that allows for global initialization easily.

I have some proposals for the way this may work:

Option 1

import sdk from "@opentelemetry/node";

// configuration object is optional, and all of its properties are optional
// Node tracer provider will be created and registered with api
sdk.configure({
  contextManager: manager, // default for node is async hooks, web is zone
  propagators: [traceContext, b3, correlation], // default is trace context
});

Option 2

import { NodeTracerProvider } from "@opentelemetry/node";

const provider = new NodeTracerProvider(/* options are unchanged */);

// configuration object is optional, and all of its properties are optional
provider.register({
  contextManager: manager, // default for node is async hooks, web is zone
  propagators: [traceContext, b3, correlation], // default is trace context
})