Default layout model deprecated

### Bug
It seems that by default docling tries to download from the hub the deprecated model "ds4sd/docling-layout-old".
In fact when I try to download the model from the hub it says that this repository is not found. And when I check the hf page for this model it is stated that it is an old model

However it is clearly stated here https://huggingface.co/ds4sd/docling-models/discussions/19 that we should rather use the "ds4sd/docling-layout-heron" one.

Is it possible to make this model as default model ?
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### Steps to reproduce
Make a convertion call using the DocumentConverter class
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### Docling version
Docling version: 2.49.0
Docling Core version: 2.46.0
Docling IBM Models version: 3.9.0
Docling Parse version: 4.2.3
Python: cpython-312 (3.12.3)
Platform: Windows-11-10.0.26100-SP0
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### Python version
Python 3.12.3
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