Add breakdown of Positively Tested Population by age

[czymra]

The Toyokeizai visualizations are going to be discontinued, or at least stop being updated from February 1st https://toyokeizai.net/sp/visual/tko/covid19/en.html

One of the most insightful visualizations there is "Tested Positive by Age" including deaths, serious conditions, hospitalized numbers and discharged numbers. I think this helps understand what is actually happening in a more detailed manner. If this data is available here, I think it would be fantastic to add this.

[reustle]

Thanks for the suggestion. If a PR is submitted with this feature, we'd be happy to review.