Automatically import updated translations from translation.io

[Floppy]

Translations on translation.io get updated pretty quick, our community are awesome, but often I forget to run the import and commit. It would be good to do this automatically, perhaps nightly, in a github action. The action should:

1. Check out the latest code
2. Run rake translation:sync to download from translation.io
3. Run i18n-tasks normalize -p to process the downloaded files into the right places
4. Commit the changes
5. Open a PR and set it to automatically merge

In an ideal world, the author of the changes would get a co-authored-by credit on the commit for their language. Currently I do this manually, I'm not sure there's a way to see who did what automatically from translation.io - perhaps crediting ALL appropriate translators on the commit for a language would be better than nothing? That could be a list hardcoded in the action, perhaps.