Use package.json instead of node-version

[misogihagi]

since setup-node v3.5, we can use nodejs version in package.json
so how can I say engines?

  "engines": {
    "node": "21.6.2"
  },

[draghtnight]

Duplicate of #

[ncalteen]

I support this in spirit, but the issue really boils down to the number of different Node.js version management tools there are (nvm, n, fnm, nodenv to name a few). The goal of this repo is to strike a balance between customizability and ease of setup. If there's a way to ensure that some of the popular node environment management tools support this as well, I'd welcome a PR :)