Add wikitablequestions dataset
@lhoestq Would you mind reviewing it when you're available? Thanks!
 > Awesome thanks for adding this dataset ! :) The dataset script and dataset cards look pretty good
> 
> It looks like your `dummy_data.zip` files are quite big though (>1MB each), do you think we can reduce their sizes ? This way this git repository doesn't become too big

I have manually reduced the `dummy_data.zip` and its current size is about 54KB. Hope it is fine for you! @lhoestq I think the dataset is ready to merge now. Any follow-up question is welcome :-D > Thanks ! It looks all good now :)

Awesome! Thanks for your quick response!