Support multilingual docs

# Context
Recently, @andygol took the initiative to translate the entire website (v3.5) to Ukrainian:
https://kubernetes.slack.com/archives/C3HD8ARJ5/p1736261563922009

In order to incorporate this work, we need to adjust the site's settings so that it handles multiple languages. This will initially involve splitting the language-specific configs into their own file. For example, taking the `menu` stuff from `/config.yaml` and put it in files like `menus.en.yaml` and `menus.uk.yaml` for English and Ukrainian, respectively.