Bring in a require-unique-dependency-names / no-dupe-deps / no-repeated-dependencies rule

[JoshuaKGoldberg]

Splitting out of #42: a few other packages in the ecosystem have some concept of a rule that detects duplicate dependencies. Let's add in an equivalent here!

• https://github.com/kellyselden/eslint-plugin-json-files/blob/3a24e6f36b7828210a56070af4487cb5831f7f24/docs/rules/require-unique-dependency-names.md
• https://ota-meshi.github.io/eslint-plugin-node-dependencies/rules/no-dupe-deps.html
• https://npmpackagejsonlint.org/docs/rules/dependencies/no-repeated-dependencies

As for the name of the rule, no-duplicate-dependencies?

Blocked on #40, but once that PR is merged this will be good to go. ✅

[github-actions]

🎉 This is included in version v0.8.0 🎉

The release is available on:

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

Cheers! 📦🚀