docs: <ContentSlot> are not supported in v3, replaced by <slot>

[lredoban]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

As mentionned in https://content.nuxt.com/docs/getting-started/migration#components are not supported in v3 so I replaced them with

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[pkg-pr-new]

npm i https://pkg.pr.new/@nuxt/content@3281

commit: 135bc39

[farnabaz]

Thanks