Store auth token in OS keychain

[hydrajump]

Which problem is this feature request solving?

AFAICT netlify-cli stores the auth token on disk in ~/Library/Preferences/netlify/config.json on macOS. Storing any secrets in plaintext on disk isn't great from a security perspective as an attacker with local system access can gain access to these secrets.

Describe the solution you'd like

It would be better to store the auth token in the operating system keychain (for macOS, Keychain) which even when unlocked, requires the user to enter their password to view the token. This is how, for example, VS Code stores the user's auth token to GitHub.

Pull request (optional)

• [ ] I can submit a pull request.