Load and display Grobid citation mention annotations

[stefanc-ai2]

https://github.com/allenai/scholar/issues/33658

Changes:

1. Added snippet to load and visualize Grobid citation mention annotations
2. Added example Grobid annotation json. You can remove this.

Example result:

I think it's easier to see the file directly than seeing the diff. https://github.com/allenai/mmda/blob/bailey_annot_grobid/end_to_end_eval_easier.ipynb

You can get the rest of the PDFs and grobid annotation at s3://ai2-s2-mmda/citation-link-evaluation-sample/