Write NDVs for Iceberg table to the Puffin files.

[amoghmargoor]

Enhancement

Currently, the statistics computed for Iceberg table will be written to native table external_column_statistics but to share it between clusters is not ideal. It needs to be computed for every cluster which needs to access the same Iceberg table. Ideally it will be great if in addition to writing statistics to external_column_statistics it also writes to puffin file. Starrocks currently can read NDVs from puffin file: enable_read_iceberg_puffin_ndv. So it would be great to even write to it. As other engine like Trino is already doing it for Iceberg format, it will be good from standardisation purpose too.

As data sketches are being used to capture NDVs in puffin file, incremental update of NDVs become possible when inserting data.

[amoghmargoor]

I am taking an initial look at the code changes needed for it.