Provide visibility to errors if segment events do not send

[ElizabethWoodhouse]

Found that we're unable to see when segment events have successfully sent: when calling analytics.track the app receives undefined as a response (even if the event has been sent successfully). When an event has not been successfully sent there have been multiple times an error gets swallowed inside analytics-next and never surface to the consuming app.

Examples:

• When sending additional eventProperties I accidentally sent data that could not be json stringified saw in the debugger that the even failed here but we did not have access to the error so an error was never thrown inside our app even though we have analytics.track wrapped in a try/catch. There's no way to have typescript catch this error prior to sending because eventProperties are type to take any value
• We were unable to see that the utm-parameter 'search' should be passed in as a string - Fix wrong utm parsing by making context.page.search the source of truth for query params. #839 so we were silently not sending events.

[marianomerlo]

Not sure if it's the same issue but it looks like very similar. I'm trying to programatically validate my segment Key:

const { Analytics } = require('@segment/analytics-node');

return new Promise((resolve, reject) => {
  new Analytics({ writeKey: 'thisIsAWrongKey' }).track(
    {
      userId: 'anonymous',
      event: 'API KEY VALIDATION',
      properties: {}
    },
    (err) => {
      if (err) {
        reject(new Error('Analytics key is invalid'));
      }
      resolve();
    }
  );
});

Internally it seems that is depends on ctx.failedDelivery() to call the callback with an error but ctx.failedDelivery() is undefined.

[jgrauel]

We have also observed that we don't get any indication when loading of analytics fails as well, it too is swallowed inside and never hits the catch block

SegmentAnalytics
    .load({ writeKey })
    .then(() => {

    })
    .catch((error) => {
      logger.warn(error, `Segment - ${callingMethodName} : Encountered error when attempting to load.`)
    })