Add a new stats tracker class AutoStatsTrackerMulti that could possibly extend AutoStatsTracker (alternatively this could be a standalone class).

It should take a 'special' leftmost namespace and an array of other namespaces for the secondary collection namespaces. It should make:

• Updates CurOp for the leftmost collection
• Updates top (via record()) for each involved namespace. This means that the same latency will be attributed to multiple collections, so it can be counted multiple times.