Add SpA-Former
# What does this PR do?

This PR adds the SpA-Former model to the 🤗 repository.

I also opened an Issue for adding the model https://github.com/huggingface/transformers/issues/19971

# Who can review?

@NielsRogge
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.<|||||>Hi @shivance do you want to proceed with this?