[core] render latex on server side

[cyrilou242]

move latex rendering to the server side. avoids the katex dependency in the html notebooks.

if we can see via some benchmarks that server-side rendering is slower than in browser, then we will have to introduce the following logic:

• in interactive mode, latex is rendered in browser
• when rendering notebooks as html, latex is rendered in the "server"

Don't want to do this before the frontend is more mature.