wip: Code to add lang tags to marian model cards
Let me know if/when you need me to review this!<|||||>Do you think it's a good investment of time to clean up automated marian model cards/conversion?

For first 1000 models from `OPUS-MT-Train` repo, the process was basically 
download and convert everything, if there is a '+' in the model name try to find a matching group name.
Automated model card is an f string + Jorg's README.

For the next 500 models, the process was:
decide whether we don't want the model ("the blacklisting process"):
- if it's "short pair" (as in en-es/en-zh) identical to one we have and the score (which we get from https://github.com/Helsinki-NLP/Tatoeba-Challenge/blob/master/models/released-models.txt) is worse than the BLEU of the previous model (which we extract disgustingly from the README.md).
- if either side is "jpx" (see slack: "you can ignore jpx"

Assuming we DO want the model:
- identical state dict conversion to the previous iteration
- Automated model card = yaml front matter with language tags (incl. group expansion for multilingual, look at all the tags on this guy: https://huggingface.co/Helsinki-NLP/opus-mt-roa-en) + f string + Jorg's README.
- also write `metadata.json` to S3 so that, in the future, blacklisting need not involved extracting floats from markdown. 


(The `api-inference` issue is a disk space one that @mfuntowicz hopes to resolve tomorrow, curl-requests come back 👍 )

This process works well but is obviously not as simple as it could/should be. The state dict automation that other projects have is simple and done, but the automated model carding needs and blacklisting needs to be at least partially rewritten.

I also suspect that if we do this again in a third repo we will need to add more model card/blacklisting logic.

### Proposed next steps
- add metadata.json to every opus-mt model in the hub
- strip the opus-mt model prefix from every model in the hub. What's the point of it?
- some one off deletions of old capital letter group names as discussed in #fixme 
- get this code clean enough that it runs on future models for the current `Tatoeba-Challenge` repo.

Did any of that make sense? What do you think?<|||||># [Codecov](https://codecov.io/gh/huggingface/transformers/pull/6586?src=pr&el=h1) Report
> Merging [#6586](https://codecov.io/gh/huggingface/transformers/pull/6586?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/28cf873036d078b47fb9dd38ac3421a7c874da44?el=desc) will **increase** coverage by `1.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/6586/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/6586?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #6586      +/-   ##
==========================================
+ Coverage   76.58%   77.61%   +1.02%     
==========================================
  Files         181      181              
  Lines       34828    34828              
==========================================
+ Hits        26674    27032     +358     
+ Misses       8154     7796     -358     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/6586?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_tf\_mobilebert.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl9tb2JpbGViZXJ0LnB5) | `24.46% <0.00%> (-72.60%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_flaubert.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl9mbGF1YmVydC5weQ==) | `24.53% <0.00%> (-63.81%)` | :arrow_down: |
| [src/transformers/modeling\_marian.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19tYXJpYW4ucHk=) | `60.00% <0.00%> (-30.00%)` | :arrow_down: |
| [src/transformers/activations.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9hY3RpdmF0aW9ucy5weQ==) | `81.81% <0.00%> (-4.55%)` | :arrow_down: |
| [src/transformers/modeling\_bart.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19iYXJ0LnB5) | `93.93% <0.00%> (-0.34%)` | :arrow_down: |
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `83.13% <0.00%> (-0.25%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `87.01% <0.00%> (+0.32%)` | :arrow_up: |
| [src/transformers/configuration\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX3V0aWxzLnB5) | `96.66% <0.00%> (+0.66%)` | :arrow_up: |
| [src/transformers/generation\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9nZW5lcmF0aW9uX3RmX3V0aWxzLnB5) | `86.46% <0.00%> (+2.25%)` | :arrow_up: |
| [src/transformers/tokenization\_utils\_base.py](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fdXRpbHNfYmFzZS5weQ==) | `93.64% <0.00%> (+3.24%)` | :arrow_up: |
| ... and [7 more](https://codecov.io/gh/huggingface/transformers/pull/6586/diff?src=pr&el=tree-more) | |

------

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