🚀 Feature: Use a shenanigans.json file instead of a "shenanigans" package.json property

[JoshuaKGoldberg]

Bug Report Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Expected

I'm finding now that there are a lot of reasons to include metadata around a package's shenanigans-manager process (e.g. #298, #299). I think it's time to make a dedicated shenanigans.json file instead of a big property in package.json files.

Additional Info

Fun fact, this was used five+ years ago, but removed in #22. At the time shenanigans.json files just included package metadata already present in package.json.