Added substreams and filenames fields to system.parts_columns table

Why it matters

This feature provides additional metadata about data parts by exposing the substreams and filenames fields in the system.parts_columns table. It helps users gain deeper insights into the structure and storage of data parts, facilitating better monitoring and debugging of data parts layout.

How to use it

Users can query the system.parts_columns table as usual to see the new substreams and filenames fields along with existing columns. No special configuration is needed to enable this feature.