[docs] Use the Hugo configuration catalog for better language management

[Andygol]

To reduce the overhead associated with managing multiple languages, I suggest switching to using a settings folder instead of the flat all-in-one hugo.html.

RE: https://gohugo.io/configuration/introduction/#configuration-directory

[chalin]

I tried that a while ago and couldn't get it to work in the way we needed, mainly due to mounts not deeply merging. Hugo has evolved since then, so it might be worth another try.