[FLINK-35982] Fix transform metadata config doesn't work if no projection block was provided

[yuxiqian]

This closes FLINK-35982.

One may readjust source table primary keys, partition keys, table options by specifying them in a Transform block like this:

transform:
  - source-table: db.tbl
    projection: '*'
    primary-keys: order_id, product_name
    partition-keys: order_id
    table-options: bucket=1

However, if the projection field is omitted (which fallbacks to default behavior that does not change any source table columns), such configuration will not take effect:

transform:
  - source-table: db.tbl
    primary-keys: order_id, product_name
    partition-keys: order_id
    table-options: bucket=1 # These options will not apply

The underlying reason is transform blocks without projection was simply ignored by PreTransformOperator, which isn't accurate since other options like primary keys, partition keys should work without projecting original columns.

[yuxiqian]

cc @ruanhang1993 @lvyanquan

[leonardBang]

+1