Support dynamic updates to existing derived columns in table

Currently Pinot doesn't support runtime changes to existing derived columns (for e.g change to ingestion transform expression) in table. Only way to make such updates is to either delete/recreate the table and ingest from scratch or add a new derived column with the changes, neither of which are ideal from usability perspective.

Can we consider improving this behavior so users can easily make adjustments to the data via table config/schema change and subsequently doing a segment reload ? cc @Jackie-Jiang @mayankshriv