function normalizeContext(context) {
  if (context.startTime) {
    const ctx = { ...context };
    ctx.startTimestamp = spanUtils.spanTimeInputToSeconds(context.startTime);
    delete ctx.startTime;
    return ctx;
  }

  return context;
}
This converts StartSpanOptions to TransactionContext.
For the most part (for now) we accept the same options,
but some of them need to be transformed.

Eventually the StartSpanOptions will be more aligned with OpenTelemetry.