fix(nuxt): NuxtLink no default rel for relative external links

[harlan-zw]

🔗 Linked issue

Relates to #25532

❓ 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

The default rel tag we apply to external NuxtLink's is quite interesting, here are some details about it if you don't know:

• We have used it because this security issue: https://mathiasbynens.github.io/rel-noopener/
• The noreferrer will automatically apply noopener, providing both are not required. I'd just use noreferrer but it's probably worth keeping consistency with larger sites in this case (i.e GitHub / Twitter still uses both).
• The noopener has been applied by default when using target="_blank" in browsers since 2021, so providing all together will not be necessary at some point.

Anyway to the point of this PR, it's to fix an edge case where it's applied when not needed and document this logic.

<template>
  <NuxtLink to="/foo" external> <!--- <a href="/foo" rel="noopener noreferrer"> -->
</template>

Wasn't sure whether to support relative links that open in a separate window context for extra security, interested to hear others' thoughts (i.e you're hosting an untrusted app on your domain).

<template>
  <NuxtLink to="/naughty-app" external target="_blank"> <!--- <a to="/naughty-app" rel="noopener noreferrer"> -->
</template>

📝 Checklist

• I have linked an issue or discussion.
• I have added tests (if possible).
• I have updated the documentation accordingly.

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