withCount columns should not be included in the cloning by default

[denitsa-md]

I have a column in the withCount property on my model:

protected $withCount = ['publications'];

When I call duplicate, cloner tries to insert that column in the table and naturally throws an sql error.

This is fixed if I add the column to $clone_exempt_attributes.

But those columns should not be included in the cloning by default because they are computed columns.