Update French translation for FAQ

It seems that this translation has gone way out of sync with the English
version, hence the larger number of edits compared with the English FAQ
update appearing in pull request zonemaster#347.

A few of the paragraphs affected by the update have been entirely
rewritten and translations revised. The French translations for DNS
terms follow Stéphane Bortzmeyer's blog post [1] commenting RFC 8499.

[1]: https://www.bortzmeyer.org/8499.html