Add Nuxt version in documentation pages

[vszakd]

Describe the feature

It would be great to add the version to which a documentation page refers to in the documentation pages for v2 and v3.

Right now, it is not possible to know to which version the pages apply without knowing beforehand. The only thing is the name (Nuxt vs NuxtJS). This, in my opinion, creates unnecessary confusion.

Thanks.

Additional information

• [ ] 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.