Add `topics` to `pubspec.yaml`

[jonasfj]

Added topics inspired by package:mono_repo.

Description

Suggestion to add topics that make it easier to discover this package and related packages.

See also: https://dart.dev/tools/pub/pubspec#topics

This is just a suggestion, you should obviously feel free to add your own topics :D

Type of Change

• [ ] ✨ feat -- New feature (non-breaking change which adds functionality)
• [ ] 🛠️ fix -- Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ ! -- Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 refactor -- Code refactor
• [ ] ✅ ci -- Build configuration change
• [x] 📝 docs -- Documentation
• [ ] 🗑️ chore -- Chore

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[jonasfj]

Closing as I can't sign the CLA without asking for a CLA-review, which I'm guessing would take a non-trivial amount of time. It also seems a bit unreasonable to ask someone for a CLA review for contributing 3 lines :rofl: