[DRAFT] feat: configurable <MotionGroup> child element variants using :config-fn prop

[BobbieGoede]

🔗 Linked issue

• docs: add documentation for <Motion> component #192 (comment)

❓ 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

This is built on #192.

This draft can be considered a feature proposal, its usefulness can be previewed in the updated docs with the following example of how easy a staggered animation would look like:

<MotionGroup preset="slideVisibleLeft" :config-fn="(index) => ({ delay: index * 200 })">
  <section>
    <h3>Product 1</h3>
    <p>Description text</p>
  </section>
  <section>
    <h3>Product 2</h3>
    <p>Description text</p>
  </section>
  <section>
    <h3>Product 3</h3>
    <p>Description text</p>
  </section>
</MotionGroup>

Not sure about the name of the prop, still need to add tests as well, feedback is appreciated!

📝 Checklist

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