Add forRootAsync for asynchronous configuration #37
Description
Hey there!
We're using nestjs-ddtrace in our project and it's been super helpful for debugging with Datadog traces. It's made a real difference!
We're running into a situation where we need to configure the module asynchronously. We're pulling our options from the Nest Config module, which in turn gets them from our .env file. A forRootAsync method would be perfect for this and would make our initialization much more flexible. This pattern is pretty common for us.
What do you think about this approach? If it sounds good to you, I'm happy to put together a PR to add this feature. Let me know your thoughts!