feat(separator): add label props on separator component

[imkhoat]

🔗 Linked issue

https://github.com/radix-vue/shadcn-vue/issues/502

❓ 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)
• [x] ✨ 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

With separator lines, sometimes we need to add a few labels or words on them. Label props were added to address this need

📸 Screenshots (if appropriate)