Support Iceberg

Iceberg isn't a normal [data format](https://clickhouse.com/docs/chdb/reference/data-formats), but is supported by separate [table functions](https://clickhouse.com/docs/reference/functions/table-functions/iceberg). Detect iceberg format and dispatch to the relevant function as appropriate.

Start by locating the code that detects data formats and dispatches to table functions, then review the linked data-format and Iceberg table-function documentation. Done means Iceberg is detected and routed to the relevant function without changing handling for other formats.

Written by the indexing model from the issue text.