EasyAdminBundle [FEATURE] Allow sorting of collections

This PR enables drag'n'drop support to order collection fields. Entities that can be sorted need a property to store the order, their collection type need such a field - and you're done :)

Add a property to the entity This is as simple as:

 /**
  * @ORM\Column(type="integer")
  */
 private int $order = 0;

Add that property to the entity type of your collection

class OrderableType extends AbstractType {
      public function buildForm(FormBuilderInterface $builder, array $options): void
      {
          $builder->add('order', IntegerType::class);
      }
}

Configure the CollectionField to be orderable

CollectionField::new('questions')
    ->setEntryType(QuestionType::class)
    ->setFormTypeOption('by_reference', true)
    ->onlyOnForms()
    ->allowDelete()
    ->setSortOrderFieldName('order')

Optionally: you can make that order field invisible, or readonly, if you don't want others to fiddle around with that setting

If you want to try it out, you can use https://github.com/NicoHaase/ea-reproducer-4293/tree/feature/test-branch-for-3645 as a fully configured environment for this feature

Closes #3645