Use added record count in cost model when rebuilding materialized view stored by iceberg

There is a cost based decision when rebuilding materialized views having aggregate.
Currently the cost model has the total count of rows of source table however incremental rebuild plan scans only the rows inserted since the last MV rebuild.

The goal is to update the row count in the cost model in case of Iceberg source tables with the sum of the added-records stored in snapshots summary since the last Mv rebuild.