Convert PyTorch checkpoint for more recent models
### Feature request

Is it possible to add more examples for model conversion between PyTorch models e.g. convert_bart_original_pytorch_checkpoint_to_pytorch.py in more recent and popular architectures? (e.g. mt5)

### Motivation

It would really accelerate setting up new feature/model development using pretained models on the database.

### Your contribution

If anyone can give feedback I am happy to share the resulting conversion script.
For each of the models added to the transformers repo, conversion scripts are created to port the weights from the original weights to the library format. You can find these under [models' respective folders](https://github.com/huggingface/transformers/tree/main/src/transformers/models) e.g. for [longformer](https://github.com/huggingface/transformers/blob/main/src/transformers/models/longformer/convert_longformer_original_pytorch_lightning_to_pytorch.py), [longt5](https://github.com/huggingface/transformers/blob/main/src/transformers/models/longt5/convert_longt5x_checkpoint_to_flax.py), or the [t5 script used for mt5](https://github.com/huggingface/transformers/blob/main/src/transformers/models/t5/convert_t5_original_tf_checkpoint_to_pytorch.py).<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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