[multistage] Tracker for Pending Planner Refactoring

[ankitsultana]

There's quite a lot of ways we can clean up the planner code still. I might not be able to address all of them immediately so tracking them here:

• Remove PinotLogicalAggregate and the corresponding PinotLogicalAggregateRule. We can do the group-trim in the Physical Planning directly. [multistage] Add Physical Plan Nodes / Trait Assignment / Logical Agg Rule #15439
• Figure out a better name than Physical* nodes. Currently, I create a partial Physical plan node and incrementally enrich it, which opens up a lot of avenues for bugs to arise and weaker semantics. see [multistage] Add Physical Plan Nodes / Trait Assignment / Logical Agg Rule #15439