Add CoNLL-2003 shared task dataset
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. 
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?