Support `options` for segment adapter

The segment `trackEvent` supports an extra `options` argument. https://segment.com/docs/sources/website/analytics.js/#track

I'd love some way to support this in the segment adapter.

In the meantime I've done something like this in the app where I need it:

```
import SegmentAdapter from 'ember-metrics/metrics-adapters/segment';
import canUseDOM from 'ember-metrics/utils/can-use-dom';
import { compact } from 'ember-metrics/utils/object-transforms';

export default SegmentAdapter.extend({
toStringExtension() {
return 'segment-extended';
},

trackEvent(options = {}) {
const compactedOptions = compact(options);
const { event, segmentOptions } = compactedOptions;

delete compactedOptions.event;
delete compactedOptions.segmentOptions;

if (canUseDOM) {
window.analytics.track(event, compactedOptions, segmentOptions);
}
}
});
```

I'd be happy to add tests and do something like this in the current Segment adapter.