Qualify column on filterable fields

[filipposallemi]

Hi, I'm wondering if make sense to have always a qualify column when a field is using filterable method.

The change should be pretty easy and require just to call qualifyColumn on the filterable attribute. This is extremely useful when you have some complex query for instance on metrics that are filterable.

   /**
     * Apply the filter to the given query.
     *
     * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
     * @param  \Illuminate\Database\Eloquent\Builder  $query
     * @param  mixed  $value
     * @return void
     */
    public function applyFilter(NovaRequest $request, $query, $value)
    {
        call_user_func($this->filterableCallback, $request, $query, $value, $query->qualifyColumn($this->filterableAttribute($request)));
    }