Adding COVID QA dataset in Chinese and English from UC SanDiego
Changed the pre-processing based on the comments raised in [PR-1482](https://github.com/huggingface/datasets/pull/1482).The below command is passing in my local environment:

`python datasets-cli test datasets/covid_qa_ucsd/ --save_infos --all_configs --data_dir ~/Downloads/Medical-Dialogue-Dataset/CovidDailogue/`

