New cluster-like command which writes to a new index than swaps,
much like is done for the data table, and only acquires
exclusive locks for said swap. This trades off disk usage for
lower contention: we hold locks for a much lower period of time,
allowing reads to work concurrently, but we have both the old
and new versions of the table existing at once, approximately
doubling storage usage while reorder is running.
Currently only works on chunks.
