🐛 Bug: Hydration script shouldn't clear existing allcontributors

[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

#441 added a hydration script that can set up an existing repository with this template's tooling. That hydration script ideally shouldn't remove any information from the repository: for example, it shouldn't wipe out the list of contributors in the .all-contributorsrc file...

Actual

...but in actuality, that's exactly what happens. 😬

The problem is that the function that generates new .all-contributorsrc content doesn't respect the existing contributors in the file, if it exists. It just creates a new file with the same content always:

https://github.com/JoshuaKGoldberg/template-typescript-node-package/blob/791332de33d8c89c62c689b9ed5ca7c10234fcb4/src/hydrate/creation/rootFiles.ts#L24-L46

Let's make the file take in any existing contributors if they exist!

Additional Info

This'll likely result in the createRootFiles function becoming async, as well as every function that calls it...

[github-actions]

🎉 This is included in version v1.28.47 🎉

The release is available on:

• GitHub releases
• npm package (@latest dist-tag)

Cheers! 📦🚀