[PLAY-1411] Badge Notification Error Variant

[kangaree]

What does this PR do?

• ✅ Add a notification error variant that's opaque and red
• ✅ Use $error in non-dark mode. Use $error_dark in dark mode.
• ✅ Update docs and testing

Screenshots:

How to test?

1. Go to kits/badge/react#notification
2. Make sure the error notification badge is the same as a notification badge, but with a different color
3. Turn on dark mode. The badge color should be red, but better suited for dark mode.
4. Make sure that the normal "colors" are not affected.
5. Repeat the above, but with Rails

Checklist:

• LABELS Add a label: enhancement, bug, improvement, new kit, deprecated, or breaking. See Changelog & Labels for details.
• DEPLOY I have added the milano label to show I'm ready for a review.
• TESTS I have added test coverage to my code.

[github-actions]

🎉 Congratulations on creating an Alpha Version!

Your Alpha for Ruby Gems is 14.0.0.pre.alpha.PLAY14113475

Your Alpha for NPM is 14.0.0-alpha.PLAY14113475