i18n(fr): add guides/syntax-highlighting.mdx & update configuration-reference.mdx

[ArmandPhilippot]

Description (required)

Adds changes from #9888:

• Translates the new guide for syntax highlighting in French
• Updates the Shiki section in configuration-reference.mdx (with a fix not yet released for backticks, see fix: typo in configuration-reference.mdx #9924)
• Updates a link in integrations-guide/markdoc.mdx

Related issues & labels (optional)

• Suggested label: i18n

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Tracked Files

Locale	File	Note
fr	guides/integrations-guide/markdoc.mdx	Localization changed, will be marked as complete.
fr	guides/syntax-highlighting.mdx	Localization added, will be marked as complete.
fr	reference/configuration-reference.mdx	Localization changed, will be marked as complete.

Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[thomasbnt]

LGTM! 🚀
Also checked the preview ✅

[yanthomasdev]

LGTM! Thanks!