Renaming repository to `nuxt/nuxt2`

[pi0]

As we introduced Nuxt 3 in nuxt/framework, it makes sense to give this repo a more sensible name to avoid confusion. nuxt2 was decided after discussing with @Atinux.

Considerations: Although GitHub should nicely handle most of the rewrites, we have to ensure it doesn't break any dependent projects that were using nuxt/nuxt.js.

Please mention if you have any concerns. Give this issue a few days before making action.