docs: update banner and badges

[DamianGlowala]

🔗 Linked issue

❓ Type of change

• 📖 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]

✅ Deploy Preview for nuxt-gtag ready!

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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?