Add default community health files?

[kenji-miyake]

It's actually not necessary since we've added them in each repository using sync-files workflow, but we can consider adding them to this repository.

https://docs.github.com/ja/communities/setting-up-your-project-for-healthy-contributions/creating-a-default-community-health-file

[kenji-miyake]

@xmfcx @BonoloAWF What do you think about it? Do you have any requests?

[xmfcx]

@kenji-miyake It's very low priority but if you want, you can add them.