i18n(fr): add guides/integrations.mdx

[ArmandPhilippot]

Description (required)

• Creates the French translation of guides/integrations.mdx based on changes from New Ecosystem tab #13571 and Fix casing and heading levels in guides/integrations.mdx #13596
• Updates the links to /guides/integrations in other pages

This basically merges the old integration-guides/index.mdx and reference/publish-to-npm.mdx but while I was there:

• I've done some rewording
• I tried to make the headings consistent (e.g. "Créer..." then "Développement de..." vs "Créer..." then "Développer...", this looks better in the TOC I think)
• The table in "Catégories" was translating the UI strings used in https://astro.build/integrations/ filters... this can be confusing. So, I added the translation between parentheses. This is not ideal with small devices because of the table, but I don't think this looks too bad.

Related issues & labels (optional)

• Suggested label: i18n

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Tracked Files

File	Note
fr/guides/integrations.mdx	Localization added, will be marked as complete.
fr/guides/on-demand-rendering.mdx	Localization changed, will be marked as complete.
fr/guides/upgrade-to/v3.mdx	Localization changed, will be marked as complete.
fr/guides/upgrade-to/v4.mdx	Localization changed, will be marked as complete.
fr/guides/upgrade-to/v5.mdx	Localization changed, will be marked as complete.
fr/reference/cli-reference.mdx	Localization changed, will be marked as complete.
fr/reference/content-loader-reference.mdx	Localization changed, will be marked as complete.
fr/reference/errors/client-address-not-available.mdx	Localization changed, will be marked as complete.
fr/reference/errors/no-matching-renderer.mdx	Localization changed, will be marked as complete.
fr/reference/modules/astro-app.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.

[ld-web]

That's CLEAN! Only 3 minor comments!
LGTM!

[ArmandPhilippot]

Looks like this is ready to go now! Thanks again for the reviews! 🙌🏽