Iceberg integration: Implement merge into iceberg table

create external table target_ice(a int, b string, c int) partitioned by spec (bucket(16, a), truncate(3, b)) stored by iceberg stored as orc tblproperties ('format-version'='2');
create table source(a int, b string, c int);

...

merge into target_ice as t using source src ON t.a = src.a
when matched and t.a > 100 THEN DELETE
when matched then update set b = 'Merged', c = t.c + 10
when not matched then insert values (src.a, src.b, src.c);