dd-trace-api-js: Node.js API package for Datadog APM

This, package, dd-trace-api on npm, exposes an API for the Datadog APM tracing library for Node.js (dd-trace).
It's meant to be used when dd-trace is installed via other means (such as Single-Step Install, other other non-npm methods) and you need an API to program against.
The API provided is completely inert unless dd-trace is installed and initialized in the same process.
You can still write code against it in that scenario, but it won't have any side effects, such as sending traces or metrics.

The API provided is as defined in the index.d.ts file. It's mostly a direct mapping of the API provided by dd-trace, but with some differences:
* The TracerProvider class for OpenTelemetry is not exported. Instead, use dd-trace's automatic insertion of TracerProvider.
* The LLM Observability APIs are not (yet) included.
* The use() method is not (yet) included.
* Anything else not documented in this repo's index.d.ts file is not (yet) included.