Use cats PairingHeap for PriorityQueueMonoid #1952
Description
PriorityQueue monoid mutates input collections and is not usable with BeamRunner. To mitigate that we disable map side aggregation for beam. We should try using cats PairingHeap implementation (https://github.com/typelevel/cats-collections/blob/master/core/src/main/scala/cats/collections/PairingHeap.scala)