Server-side meta tags

[laem]

Bug Report

Problematic behavior
It looks like the meta tags are loaded on the client side, not readable by e.g. opengraph.xyz
Example doc : https://docs.numerique.gouv.fr/docs/1b64643b-7163-4a96-b78d-251f3a5e81e7/

My guess is that this PR did use something like React Helmet, client-side.
#224

Expected behavior/code
Metatags should be generated on the server. It is very important to share intelligible links, and to find the doc in your browser history.

Steps to Reproduce

1. Share this link on a platform that shows link vignettes (e.g. mattermost)
2. No doc title is shown

Possible Solution
In NextJS, add metatags to page.tsx