Spright-related CODEOWNERS and spec template updates

[m-akinc]

Pull Request

🤨 Rationale

Part of #1979

👩‍💻 Implementation

• Some updates to CODEOWNERS (keeping same owners for Spright as for Nimble)
• Marked some items/sections optional for Spright in spec templates

🧪 Testing

N/A

✅ Checklist

• [x] I have updated the project documentation to reflect my changes or determined no changes are needed.

[m-akinc]

Assuming buddy review unnecessary.