Support for pointer-generator architectures.
# 🚀 Feature request

Is there interest in adding pointer generator architecture support to huggingface? These are currently supported in [fairseq](https://github.com/pytorch/fairseq/blob/master/examples/pointer_generator/README.md), and in general should not be terrible to add for most encoder-decoder seq2seq tasks and modeks.

## Motivation

Pointer-generator architectures generally give SOTA results for extractive summarization, as well as for semantic parsing. (See for instance this paper [https://arxiv.org/pdf/2001.11458.pdf](url)).

## Your contribution
If there is interest but not bandwidth from huggingface members, I could try to add pointer-generator support for a specific architecture such as the T5 and see how hard it would be to port over fairseq's implementation for instance.

Note: apologies also if I've missed where huggingface supports it already.

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/master/CONTRIBUTING.md) are likely to be ignored.