dt/datalake: Integration testing for schema compat integration

test that:
- table schema updates work
- valid evolved schemas are backwards compatible w/ historical rows
- adding columns never read existing values from another column

todo:
- dropping a column does not change the values in any other column
- updating a column or field does not change values in any other column
- changing the order of columns or fields in a struct does not change the
  values associated with a column or field name

Signed-off-by: Oren Leiman <[email protected]>