Insert Extractive QA templates for SQuAD-like datasets
hi @lhoestq @SBrandeis i've now added the missing YAML tags, so this PR should be good to go :) urgh, the windows tests are failing because of encoding issues 😢 

```
dataset_name = 'squad_kor_v1'

    @pytest.mark.parametrize("dataset_name", get_changed_datasets(repo_path))
    def test_changed_dataset_card(dataset_name):
        card_path = repo_path / "datasets" / dataset_name / "README.md"
        assert card_path.exists()
        error_messages = []
        try:
            ReadMe.from_readme(card_path)
        except Exception as readme_error:
            error_messages.append(f"The following issues have been found in the dataset cards:\nREADME:\n{readme_error}")
        try:
            DatasetMetadata.from_readme(card_path)
        except Exception as metadata_error:
            error_messages.append(
                f"The following issues have been found in the dataset cards:\nYAML tags:\n{metadata_error}"
            )
    
        if error_messages:
>           raise ValueError("\n".join(error_messages))
E           ValueError: The following issues have been found in the dataset cards:
E           README:
E           'charmap' codec can't decode byte 0x90 in position 2283: character maps to <undefined>
E           The following issues have been found in the dataset cards:
E           YAML tags:
E           'charmap' codec can't decode byte 0x90 in position 2283: character maps to <undefined>
``` Seems like the encoding issues on windows is also being tackled in #2418 - will see if this solves the problem in the current PR
This PR adds task templates for 9 SQuAD-like templates with the following properties:

* 1 config
* A schema that matches the `squad` one (i.e. same column names, especially for the nested `answers` column because the current implementation does not support casting with mismatched columns. see #2434)
* Less than 20GB (my laptop can't handle more right now)

The aim of this PR is to provide a few datasets to experiment with the task template integration in other libraries / services. 

PR #2429 should be merged before this one.

cc @abhi1thakur 