Support packing upgrade track clusters

When persisting tracks in Run 2 we persisted all tracking station clusters associated to them. We can't do this for Upgrade data because the TrackClonerWithClusters algorithm doesn't support cloning clusters from Upgrade detectors.

It would be useful to support for this. Although we might end up not using today's packers, they're all we have for estimating Upgrade event sizes. Not supporting track cluster packing means we underestimate the event size.