feat: ExportColumn visibility

[billmn]

Description

Introduces the ability to set an ExportColumn as visible or hidden.

Example:

ExportColumn::make('price')
    ->visible(fn (): bool => auth()->user()->can('seePrice')),

ExportColumn::make('price')
    ->hidden(fn (): bool => auth()->user()->cannot('seePrice')),

It could also be useful add a method on ExportAction and ExportBulkAction (eg. showVisibleTableColumnsByDefault()) that automatically mirrors the visibility conditions already defined on the corresponding TableColumn, avoiding the need to repeat the same visibility logic in both places.

This would be similar to how enableVisibleTableColumnsByDefault() already syncs which columns are enabled by default based on table column visibility.

Functional changes

• Code style has been fixed by running the composer cs command.
• Changes have been tested to not break existing functionality.
• Documentation is up-to-date.