always persist pending attachments when using with spatie/nova-translatable

[xdiaoa]

What I am trying to do
I am trying to use this package with spatie/nova-translatable package.
Something like this

use Froala\NovaFroalaField\Froala;
use Spatie\NovaTranslatable\Translatable;

Translatable::make([
    Froala::make('Biography')->withFiles('public'),
]),

The problems

• Problem 1
  When images are selected and sent to be stored as a pending attachment, FroalaUploadController's store method return 404. The problem lies with the spatie/nova-translatable package for which I created a PR here.
• Problem 2
  This problem arises after the Problem 1 is solved. Imagine we got around the Problem 1 by overriding a base Translatable class as the following.

<?PHP

namespace App\Nova\Fields;

use Illuminate\Contracts\Validation\Rule;
use Laravel\Nova\Fields\Field;
use Spatie\NovaTranslatable\Translatable as SpatieTranslatable;

class Translatable extends SpatieTranslatable
{

    protected function createTranslatedField(Field $originalField, string $locale): Field
    {
        $originalAttribute = $originalField->attribute;
        $translatedField = parent::createTranslatedField($originalField, $locale);
        $translatedField->attribute = 'translations_'.$originalAttribute.'_'.$locale;

        return $translatedField;
    }
}

When images are selected, the images are saved pending attachments. But when submitting the form, the pending attachments will not be persisted. This is because Translatable's createTranslatedField method defines a fillUsing callback on every translatable field. And the fillAttribute on Froala will just check if there exists a fill callback and executes and returns that. (It will not persist the pending attachments there as expected).
So in this PR, what I did is to run a callback if it exists and then always persist the pending attachments in fillAttribute.

See this sample project's nova-translatable-with-froala branch to quickly check the issues.

Note: This PR depends on the spatie/nova-translatable PR to be merged.

Thanks :)