Allow to explicitly specify metadata file

Why it matters

This feature addresses the need to directly control which Iceberg metadata file is read, enabling more precise data handling and troubleshooting. It improves flexibility and reliability when working with Iceberg tables in ClickHouse by allowing explicit metadata file specification.

How to use it

Set the iceberg_metadata_file_path setting with the desired metadata file path when creating or querying Iceberg tables using the storage or table function, for example:

SET iceberg_metadata_file_path = 'path/to/metadata/file';
SELECT * FROM iceberg_table;