add wit dataset
Opening this up - Here's whats left to make it really shine:
- [ ] Update dataset card (this is being worked on by the author)
- [ ] Add `dataset_info.json`. Requires downloading the entire dataset. I believe @lhoestq mentioned he may have a machine he's using for this sort of thing.

I think both of these _could_ be done in separate PRs, but I'm not picky either way.

Also, we may find that users (and/or the authors) would like additional configurations for languages, image only, embeddings only, etc. I think we can wait and see what the community says on this and address in different PR. Finally got around to this PR, sorry for the delay!

I added some minimal info to the dataset card so we can at least have it on the hub and work more on it later.

Unfortunately, this re-triggered the tests and it looks like we need a rebase? cc @nateraw  Yea we need to rebase. Also I think it would be best to update the features to all be strings to match the original datasets format. I ran into a lot of issues with incorrect data types deep into the Dataset info Json process because it couldn't cast correctly. 

I mentioned this to @mariosasko - he might pick up this PR if I don't have bandwidth to finish soon. 
Resolves #2902 based on conversation there - would also close #2810. Open to suggestions/help 😀

CC @hassiahk @lhoestq @yjernite 