Pass `extends` via CLI

[dword-design]

Describe the feature

I think it would be great to pass the extends field via the CLI (nuxt build, nuxt dev). It would clean up nuxt.config.js and the Nuxt call could be refactored away.

So I could do something like this: nuxt dev --extends @me/nuxt-config and start with no nuxt.config.js.

Additional information

• [x] Would you be willing to help implement this feature?
• [ ] Could this feature be implemented as a module?

Final checks

• [X] Read the contribution guide.
• [X] Check existing discussions and issues.