Add Iceberg catalog config property to set iceberg.worker.num-threads

[osscm]

related issue: #11708 comment: #11708 (comment)

TableScan::planFiles

executed in a shared Iceberg worker pool. It's shared among queries so high concurrency of metadata-heavy queries can make things worse. And this thread pool is not managed by Trino so its memory usage is not tracked.

so, we should allow this property to be passed from the catalog, so that it will not be set statically.

[electrum]

I think this needs to be fixed in the Iceberg library to allow per-catalog configuration rather than relying on a global system property. I don't see a way to fix this on the Trino side.

[raunaqmorarka]

There is a planWith(ExecutorService executorService) API available, which we are using in IcebergSplitSource (configurable though Make Iceberg split manager threads configurable).
We could extend it's usage to all callers of planFiles to control number of threads on Trino side.