Version dropdown menu

[begleynk]

While Docapella won't have native versioning support (as in, handling multiple versions of your docs in the same branch), we should support adding links to your other docs versions.

This would mean you could have your docs hosted e.g. as v2.docs.example.com, v3.docs.example.com, and docs.example.com for latest, as separate Docapella project. Then you'd create a versions dropdown menu in each one pointing to one another.

Something like this in the docapella.yaml:

versions:
  - label: 3.0
    current: true
  - label: 2.0
    href: v2.docs.example.com
  - label: 1.0
    href: v1.docs.example.com