Corepack Support

Description:
Support using https://github.com/nodejs/corepack to manage non-NPM package managers.

Ideally in between installing node and bootstrapping the package manager cache, this action:

• enables corepack (could be a no-op depending on the node version)
• caches/restores the corepack root
• runs corepack prepare --active

(after some research, that last one may not necessary but instead makes an implicit step explicit)

This behavior could either be trigged by the presence of the packageManager field in the root package.json (might be suprising), cache: 'auto' as possibly envisioned in #306, or corepack: true

Justification:
Both pnpm and yarn support corepack, and yarn recommendeds corepack for package manager versioning. Currently using corepack with this action will break when using the cache key as this action assumes the appropriate version manager has already been installed. However, you don't necessarily want to bootstrap with corepack until the appropriate node version has been installed and configured.

Related: #530 #182

Are you willing to submit a PR?
Yes

Start by reviewing the setup-node caching and package-manager bootstrap flow described in this issue, then inspect how the root package.json packageManager field could drive behavior. Compare the proposed corepack: true, cache: 'auto', and automatic-detection approaches, including enabling Corepack, restoring its root, and running corepack prepare --active; done means the selected behavior works with pnpm or Yarn caching without requiring a preinstalled package manager.