Optional policyDefault 'preferred'.
Optional seedFor 'weighted' and 'random': fixes the sequence of seatings this
instance produces, call after call. A whole number from 0 to 4294967295,
or a non-empty string.
Optional distinctKeep seats on different vendors, providers or models while the pool allows it.
Default 'vendor' under panel and parallel, false under the other strategies.
How pooled seats are filled from the pool.