fix: Use YaruInfoBox for notification boxes

[ashuntu]

This effectively aligns the colors correctly with what is used by Yaru for info boxes, which you can see at https://ubuntu.github.io/yaru.dart under the "YaruInfo" tab. Our colors in light mode were identical to Yaru, but dark mode colors were not. This fixes that issue and simplifies the widget code significantly by just using the YaruInfoBox.

This page still needs more changes in the future, but this should be sufficient for notification colors for the time being.

	Dark	Light
Existing
New

---

UDENG-5590

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 89.41%. Comparing base (d5ce322) to head (2d03b1d).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
...bscription_status/subscription_status_widgets.dart	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1010      +/-   ##
==========================================
+ Coverage   89.38%   89.41%   +0.03%     
==========================================
  Files         113      113              
  Lines        7618     7606      -12     
==========================================
- Hits         6809     6801       -8     
+ Misses        632      629       -3     
+ Partials      177      176       -1     

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[ashuntu]

We miss some opportunity for tests here, where we could mock a launch event for the success link. However, this page is changing somewhat significantly, so I don't think it would be worthwhile for a test for that right now (it wasn't covered previously, anyway).

[CarlosNihelton]

What a lovely diff! :)