Add the DKTC dataset (Extension of #3564)
I reflect your comment! @lhoestq  Wait, the format of the data just changed, so I'll take it into consideration and commit it. I update the code according to the dataset structure change. Thanks ! I think the dummy data are not valid yet - the dummy train.csv file only contains a partial example (the quotes `"` start but never end). > Thanks ! I think the dummy data are not valid yet - the dummy train.csv file only contains a partial example (the quotes `"` start but never end).

Hi! @lhoestq There is a problem.  
<img src="https://user-images.githubusercontent.com/42150335/149804142-3800e635-f5a0-44d9-9694-0c2b0c05f16b.png" width=500>
  
As shown in the picture above, the conversation is divided into "\n" in the "conversion" column.  
That's why there's an error in the file path that only saved only five lines like below. 

```
'idx', 'class', 'conversation'
'0', '협박 대화', '"지금 너 스스로를 죽여달라고 애원하는 것인가?'
아닙니다. 죄송합니다.'
죽을 거면 혼자 죽지 우리까지 사건에 휘말리게 해? 진짜 죽여버리고 싶게.'
정말 잘못했습니다.
```
   
In fact, these five lines are all one line.  
  

 Hi ! I see, in this case ca you make sure that the dummy data has a full sample ?

Feel free to open the dummy train.csv in the dummy_data.zip file and add the missing lines Sorry, I'm late to check! I'll send it to you soon!
New pull request of #3564. (for DKTC)
