OpenTelemetry exports can send traces

Add "traces" to an export's signals and every API call your account makes, including creates, commands, file calls, pauses, wakes and snapshots, is sent to <endpoint>/v1/traces as an OTLP span within about a second, with the OpenTelemetry HTTP attributes and the request ID. A call that carries a W3C traceparent header becomes a child of the caller's span; the TypeScript and Python SDKs send that header automatically when OpenTelemetry is set up in your process. Exports now report exportedSpans, and the span pushes' own health in tracesLastSuccessAt, tracesLastError and tracesFailures, apart from the logs' and metrics' lastError and failures. The default signals are unchanged (traces).