Add CoNLL-2003 shared task dataset
I think we should somewhere mention, that is the dataset in IOB2 tagging scheme, whereas the original dataset uses IOB1 :) Indeed this is something we want to mention.

If would want to add more details about the IOB1->2 change, feel free to ignore my suggestions and edit the description + update the dataset_info @lhoestq do you want me to update it or you'll update it. I am ok either way The best would be to mention this change in the description and then update the dataset_info.json file.
Could you do that if you don't mind ?

Then it should be ready to merge :)

Thanks again for adding this dataset ! No problem @lhoestq I'll do the update @lhoestq please check if 847addf is exactly what we want Is the German task also part of this? If not, can it be accessed via the Datasets library?
Please consider adding CoNLL-2003 shared task dataset as it's beneficial for token classification tasks. The motivation behind this PR is the [PR](https://github.com/huggingface/transformers/pull/7041) in the transformers project. This dataset would be not only useful for the usual run-of-the-mill NER tasks but also for syntactic chunking and part-of-speech (POS) tagging. 