Add task templates for tydiqa and xquad
Just tested TydiQA and it works fine :)
This PR adds question-answering templates to the remaining datasets that are linked to a model on the Hub.

Notes: 

* I could not test the tydiqa implementation since I don't have enough disk space 😢 . But I am confident the template works :)
* there exist other datasets like `fquad` and `mlqa` which are candidates for question-answering templates, but some work is needed to handle the ordering of nested column described in #2434 

