[Object Detection model] Please implement convnext

[convnext](https://torchvision.mlverse.org/dev/reference/model_convnext) classification model is currently available in {torchvision}, but there is a also a [Object Detection head](https://github.com/facebookresearch/ConvNeXt/tree/main/semantic_segmentation/configs/_base_/models) that could be ported here.