Add Eloquent `apiProperties`

[soyuka]

Description
We want to add ApiProperty to Eloquent models. To do so (inspired by https://github.com/api-platform/core/pull/4197) we will add a protected $apiProperties on an Eloquent Model:

class Book extends Model {
    protected $apiProperties = ['name' => new ApiProperty(...)];
}

These need to be read by the Laravel specific PropertyMetadataFactories.

https://github.com/api-platform/core/pull/5882