[Feature Request] Filter for only certain columns on pscale database dump

[davidzajac1]

It would be helpful to be able to filter for only certain columns from certain tables when calling pscale database dump. Currently there's only a --tables flag to only dump certain tables and a --wheres flag to filter out rows.

Could be a --columns flag or an option within the --tables flag to pass in an object instead of just strings like --tables "{'sometable': ['col1', 'col2'], 'sometable2': ['col3']}"