Entity Linking 
This pull request **introduces 18 alerts** when merging aed6db426bd95772754fe44ad564645ee494a9c1 into 179d49ff4f1998df60f8ccefa6ddb8a5f95ad674 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-ea22ab685b5a0f77bf123ef856320f3ae6314173)

**new alerts:**

* 16 for Unused import
* 1 for Redundant assignment
* 1 for Wrong number of arguments in a call This pull request **introduces 18 alerts** when merging 6f7912bcc5d53fd03105582eed850f1945082b2f into 179d49ff4f1998df60f8ccefa6ddb8a5f95ad674 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-e06c749c33bf16ec168789a203ee5c44e26719c2)

**new alerts:**

* 16 for Unused import
* 1 for Redundant assignment
* 1 for Wrong number of arguments in a call Please ping me offline - let's put the tiny dataset on AWS rather than GitHub repo.
Regarding DCO, when you commit, please add "-s" flag to do signoff on your commits. To sign already committed commits, checkout DCO's bot output https://github.com/NVIDIA/NeMo/pull/2042/checks?check_run_id=2309052982 
 This pull request **introduces 18 alerts** when merging 0ebb5d40f18a73e9464e8cec6e31a43d978097d5 into 52121810b428e011666e656d313b42c954def26b - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-ba0cf96127b08d3fce0f2d80a181abe2afdac28a)

**new alerts:**

* 16 for Unused import
* 1 for Redundant assignment
* 1 for Wrong number of arguments in a call
This PR adds a new model, dataset, loss, training example code and notebook demo for entity linking. The loss and model are an implementation of the "Self-Alignment Pretraining for Biomedical Entity Representations" paper.