Update documentation website

[rien]

This PR updates dolos.ugent.be for some changes added in Dolos v2.5:

• Rename /guide pages to /docs
• Rename /try pages to /demo
• Add relevant video's showcasing Dolos
• Update references to dodona.ugent.be to dodona.be
• Explain how dolos-parses works, update text to reflect how new languages can be added
• Add a contact page on /about/contact
• Add a documentation page about how to self-host the web-app /docs/hosting-dolos
• Update to most recent vitepress version