migrate user documentation

[yksflip]

wip
see #1170

feel free to jump in

• copy docs from https://github.com/foodcoops/user-docs
• setup vitepress
• setup ci + github pages
  • https://vitepress.dev/guide/deploy#github-pages
  • need to come back to this after merged to master
• add basic english translation and make it default
• do some more cleaning on the existing documentation

after merge:

• redirect the https://docs.foodcoops.net to new github pages site
• archive https://github.com/foodcoops/user-docs
• adapt all references to new user docs
• remove this branch from the github action / allowed deploy branches (should be master only)

[yksflip]

at the moment the deployment goes here https://foodcoops.net/foodsoft/ (the path equals the reponame ..)
once we feel ready on this one, we should

1. change the dns record of docs.foodcoops.net point to foodcoops.net (points to gh-pages)
2. configure docs.foodcoops.net as a custom domain in this repo settings
3. remove the base path in .vitepress/config.mts

[yksflip]

@mjavurek , I saw that you've been working on the user docs lately, would be happy if you could provide feedback on this :)