json reader DCHECK fail because of missing TYPE_STRING
fix bug that if no file is found, the tvf will throw NPE.
The predicate conjuncts can not be pushed down to parquet reader if this is a load task.
Because the predicate should be applied on column of dest table, not on column of source file.
Add a temp property "use_new_load_scan_node" of broker load to make regression test happy.
So that we can use new load scan node for a certain job and avoid setting global FE config.