Add the stats needed to support `printPlanWithStats`

[GregoryKimball]

Description

We received a request from Presto C++ to add TaskStats and OperatorStats to the cuDF operators. Let's please add the stats needed to support printPlanWithStats (https://facebookincubator.github.io/velox/develop/debugging/print-plan-with-stats.html)

[GregoryKimball]

@devavret would you please work through the stats requirement for one operator? Then let's look at the draft and decide how to involve Vinith