Update for Iceberg table engine

Why it matters

This feature introduces support for the ALTER UPDATE command on tables using the Iceberg engine in ClickHouse. It solves the problem of modifying existing records in Iceberg tables, enabling users to update data efficiently and directly within the table without requiring full rewrites or complex workarounds.

How to use it

Users can perform updates on Iceberg tables using the ALTER UPDATE syntax just like with other table engines. For example:

ALTER TABLE my_iceberg_table UPDATE column = value WHERE condition