Add rgpd cookie banner to both doc and website.

[MatthieuVates]

Before submitting the pull request, you must agree with the following statements by checking both boxes with a 'x'.

• "I accept that my contribution is placed under the CC BY-SA 2.0 license [1]."
• "My contribution complies with the Developer Certificate of Origin [2]."

[1] https://creativecommons.org/licenses/by-sa/2.0/
[2] https://docs.xcp-ng.org/project/contributing/#developer-certificate-of-origin-dco

Sorry for the changes of quote type in docusaurus.config.js.
It seems that there's no prettier file for the repo and that i don't have the same default than the previous editor.

[Marcpezin]

@stormi It looks good to me, but I don't want to merge it myself to avoid creating any conflict as it's now a 2 weeks commit, not sure if it should be rebased first :/