Save & load sparse models from the models database
# 🚀 Feature request

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     Please provide a link to the paper and code in case they exist. -->

Handle saving and loading pipeline for sparse models such as PruneBERT.

## Motivation

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     related to a problem? e.g., I'm always frustrated when [...]. If this is related
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New sparse models will be extremely useful if we can use them by downloading the compressed. version with the `.from_pretrained` functions

## Your contribution

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An example is already part of the current repo so I can try to create a PR later: https://github.com/huggingface/transformers/blob/master/examples/movement-pruning/Saving_PruneBERT.ipynb

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
