docs: update banner and badges

[DamianGlowala]

🔗 Linked issue

❓ Type of change

• [x] 📖 Documentation (updates to the documentation, readme or JSDoc annotations)
• [ ] 🐞 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)
• [ ] 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Prepares the module for migrating under the @nuxtjs/gtag namespace.

📝 Checklist

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

[netlify[bot]]

✅ Deploy Preview for nuxt-gtag ready!

Name	Link
🔨 Latest commit	6b7a34a1622299e0acc109bcfdc8170b875c7521
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[johannschopplich]

Wow, thanks for the work on the banner!

Let's wait until this module has been moved to the @nuxtjs namespace, shall we?