adding covid-tweets-japanese
I think it's because the file you download uncompresses into a file and not a folder so `--autogenerate` couldn't create dummy data for you. See in your dummy_data.zip if there is a file there. If not, manually create your dummy data and compress them to dummy_data.zip. @cstorm125 Thank you for the comment! 
As you point out, it seems my code has something wrong about downloading and uncompressing the file.
However, my manually created dummy data seems to contain a file of the required format.

On Colaboratory,
`!unzip /content/datasets/datasets/covid_tweets_japanese/dummy/1.1.0/dummy_data.zip`
returns:

```
Archive:  /content/datasets/datasets/covid_tweets_japanese/dummy/1.1.0/dummy_data.zip
   creating: content/datasets/datasets/covid_tweets_japanese/dummy/1.1.0/dummy_data/
 extracting: content/datasets/datasets/covid_tweets_japanese/dummy/1.1.0/dummy_data/data.csv.bz2  
```

The original data is `data.csv.bz2`, and I had a very hard time dealing with uncompressing bzip2.
I think I could handle it, but there may be problems remain.
Adding COVID-19 Japanese Tweets Dataset as part of the sprint.

Testing with dummy data is not working (the file is said to not exist). Sorry for the incomplete PR.