Add Fallback Locale and Additional Query Support to findBySlug

[mkeremcansev]

Add Fallback Locale and Additional Query Support to findBySlug

This PR enhances the findBySlug method in the HasSlug trait by introducing two key features:

1. Fallback Locale Support

• If the model uses the HasTranslatableSlug trait, the method now checks for a matching slug in both the current locale and the fallback locale (defined in the application's fallback_locale configuration).

2. Additional Query Customization

• A new $additionalQuery parameter has been added, allowing developers to pass a callable to customize the query further.

Example Use Case:

$model = MyModel::findBySlug('example-slug', ['id', 'name'], function ($query) {
    $query->where('status', 'active');
});

[freekmurze]

Thanks!