docs(components): Add info about `extensions` and `pathPrefix` keys

[MorevM]

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🔗 Linked issue

#8922 (closed but there were a comments with explanations)

❓ Type of change

• [x] 📖 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

Documentation for extensions and pathPrefix keys of components > dirs objects of nuxt.config.ts

📝 Checklist

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

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[MorevM]

@danielroe I wrote a docs as promised in nuxt/nuxt.js#15447

Spelling corrections are welcome, also I'm not sure should I use object form of components key in docs or not?

// This one
components: [
  { path: '...' },
],

// or this one
components: {
  dirs: [
    { path: '...' },
  ]
}

[danielroe]

merged in https://github.com/nuxt/framework/commit/28a2a91b64e16d499c69da1a1fb54871992b3b14.