Add min/max values for the non-primary key columns in the metadata of rowsets/datablocks

It's possible to add min/max values for the non-primary key columns in the metadata of diskrowset/datablock, and then we can skip decoding/evaluating the unnecessary diskrowset/datablock while scanning. Just like the "compute stats" feature on impala, and the only difference is that kudu supports updates. So, the min/max values should be invalid if the columns that have deltas while scanning.