Resize position embeddings in PreTrainedModel
### Feature request

Add a method to resize position embeddings in PreTrainedModel, in the same way as there is `resize_token_embeddings` for word embeddings.

There are several ways to do that:
- retrain everything from scratch
- keep the pretrained embeddings but add new trained from scratch for the new positions (as done in `PreTrainedModel._get_resized_embeddings` if I understand correctly)
- same but initialize new positions by interpolating pretrained ones instead of random init

### Motivation

It would be nice to be able to resize position embeddings when the PreTrainedModel has too small `max_position_embeddings`.
I found several related issues:
- https://stackoverflow.com/questions/69820065/how-to-extend-a-pretrained-transformer-model-configured-with-small-max-position
- https://github.com/huggingface/transformers/issues/1978

### Your contribution

Willing to help :)
From what I can tell, most of the job is already done in `PreTrainedModel._get_resized_embeddings` 
I have met the same issue.<|||||>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.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.<|||||>I am also facing the same issue<|||||>is this issue resolved? Why was it closed?  I need to use different size, not, but I can't do it<|||||>It was closed automatically because no one answered after one month :man_shrugging: 
