[model_cards] Migrate cards from this repo to model repos on huggingface.co
Fellow reviewers/contributors, please take a look at the documentation part and let me know your thoughts.

---
#### ⚠️ Still to-do before merging ⚠️ 
- [x] Post a message on the Forum: https://discuss.huggingface.co/t/announcement-all-model-cards-will-be-migrated-to-hf-co-model-repos/2755
- [x] Update the buttons on the model pages
- [x] merge all out-standing model card PRs on the transformers repo
- [x] the actual migration into the hf.co model repos

ETA: I plan on doing this Thursday (Dec 10) or Friday (Dec 11)!
@patrickvonplaten, unless we erase them from the history, it won't make git clone any faster.<|||||>@sgugger it might make a `git checkout` slightly faster. I don't think the model cards were ever an issue in terms of git performance though (8% of number of files in the repo, 7% of total size of the repo)

<|||||>https://github.com/github/git-sizer is an awesome tool by the way

```
$ git-sizer
Processing blobs: 22486                        
Processing trees: 25585                        
Processing commits: 7749                        
Matching commits to trees: 7749                        
Processing annotated tags: 33                        
Processing references: 216                        
| Name                         | Value     | Level of concern               |
| ---------------------------- | --------- | ------------------------------ |
| Biggest checkouts            |           |                                |
| * Maximum path length    [1] |   135 B   | *                              |

[1]  030c0d2cdc80cf8dcf23a6ee55c20e979548a181 (refs/heads/master^{tree})
```

vs on datasets (cc @lhoestq):
```
$ git-sizer
Processing blobs: 9449                        
Processing trees: 12905                        
Processing commits: 1245                        
Matching commits to trees: 1245                        
Processing annotated tags: 16                        
Processing references: 110                        
| Name                         | Value     | Level of concern               |
| ---------------------------- | --------- | ------------------------------ |
| Biggest objects              |           |                                |
| * Blobs                      |           |                                |
|   * Maximum size         [1] |  17.8 MiB | *                              |
|                              |           |                                |
| Biggest checkouts            |           |                                |
| * Number of directories  [2] |  4.89 k   | **                             |
| * Maximum path depth     [3] |    16     | *                              |
| * Maximum path length    [3] |   231 B   | **                             |

[1]  3fe8eaab7a337ea2a8d06daa5721fc5935ba3098 (75cafce7677d6f66c49c34e43cfbc425e1f50d30:datasets/anli/dummy/plain_text/0.1.0/dummy_data.zip)
[2]  681c565a3d8f63535823a1d33438c2b76ba3c706 (refs/heads/master^{tree})
[3]  c94ea70f34be4ed2723fc1c647340792ba03879c (7cd045237bb77f3b32877d31aae87789ec57ffab^{tree})
```<|||||>**Update**: I deployed the new buttons/call to actions on the model pages. 
I also created a new Forum topic (@sgugger @Pierrci @patrickvonplaten) titled "Model cards" where users can suggest edits or creations of existing model cards, in case they don't have write access to the corresponding model repo:

https://discuss.huggingface.co/t/about-the-model-cards-category/2777<|||||>All out-standing model card PRs were merged. No more model cards PRs expected!

Will migrate existing ones now.