DiffusionDet: Diffusion models for object detection

### Model/Pipeline/Scheduler description

Recent work which leverages diffusion models for object detection task. https://arxiv.org/abs/2211.09788

Add capability to run it through HF diffusers pipeline and if possible also create benchmarks or comparison on datasets like nuScenes.

### Open source status

- [X] The model implementation is available
- [ ] The model weights are available (Only relevant if addition is not a scheduler).

### Provide useful links for the implementation

_No response_

Start with the linked DiffusionDet paper and locate the existing model implementation. Assess how it could be exposed through an HF diffusers pipeline, then investigate whether comparison benchmarks on datasets such as nuScenes are feasible; done would mean a working integration and, if feasible, documented benchmark results.

Scritto dal modello di indicizzazione a partire dal testo della issue.