Support GitHub rendering CSV

[pr1v4cy]

GitHub can render tabular data from .csv-Files. But it only supports comma-delimited files.
So every .csv would need a change, and probably some changes in the backend are needed.
I don't know whether the effort is worth the added value.

I changed one file as test. I also split up the German and English names in extra columns.

src/de/holidays/holidays.school.sh.csv

More information:
https://docs.github.com/en/repositories/working-with-files/using-files/working-with-non-code-files#rendering-csv-and-tsv-data

[fstueber]

Thanks for feedback. Its on my list. And: Your pull request is also not forgotten.

[fstueber]

See: openpotato/openholidaysapi.website#39 (comment)