feat: provide npm registry customization

[antongolub]

zx has internal feature to install package (see deps.ts and cli.ts), but the registry path is hardcoded. Let's make it configurable via the CLI opts too.

zx --install-registry='https://npm-proxy.example.com' script.mjs

[easymikey]

I’m ready to take on the task.

[antongolub]

Go ahead!