Adding support for Iceberg

[luss]

Apache Iceberg is all the rage and the pyiceberg pypi project is a pure python interface to it that is well supported. Iceberg is missing a front end SQL layer (depends on sparkSQL or ...) and I think Postgres being that layer ala Multicorn2 is an idea with legs. Anyone else interested?? We could consider the radical step to make this support part of this core project rather than a seperate project.