docs: upgrade docusaurus from version 3.8 to 3.9
The onBrokenMarkdownLinks option is deprecated and has been replaced by siteConfig.hooks.onBrokenMarkdownLinks. However, since the option was configured to 'warn' and is the default behavior for this option, deleting the onBrokenMarkdownLinks seems like easier
Signed-off-by: Thomas Moraine <thomas.moraine@vates.tech>
Migrate docs from VuePress wich is not maintained anymore, to Docusaurus, which is maintained and also used fro XCP-ng docs.
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Co-authored-by: Thomas Moraine <thomas.moraine@vates.tech>
