🚀 Feature: Add packageManager back to the root package.json

[JoshuaKGoldberg]

Bug Report Checklist

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

Overview

Coming over from JoshuaKGoldberg/create#145:

Consider adding packageManager to the root package.json, since it was unclear which version of pnpm was needed (I had the wrong one and had to upgrade)

Agreed, it's irksome having to guess which package manager & version to use. You can kind of clue in which package manager it is from the lockfile existing, but that's manual. And the version is very much educated-guesswork.

Additional Info

This actually used to exist in this repo, but I removed it:

1. 🐛 Bug: Crash in --mode create if pnpm version mismatches  #1513
2. fix: remove package.json packageManager field #1529

This was discussed in pnpm/pnpm#8087, and at the time of #1529, still open - hence the removing of the field in this repo. It was later resolved in pnpm/pnpm#8166. Phew! So we are unblocked in this repo.

🎁

Co-authored-by: @boneskull

[JoshuaKGoldberg]

@all-contributors please add @boneskull for ideas.

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[allcontributors]

@JoshuaKGoldberg

I've put up a pull request to add @boneskull! 🎉