Set name of current route as transaction

[ueman]

📜 Description

This change adds the current route as SentryEvent.transaction.

💡 Motivation and Context

https://develop.sentry.dev/sdk/event-payloads/ suggests to use the current route as transaction name.

💚 How did you test it?

Unit tests

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.21%. Comparing base (35378c9) to head (058a7f9).
Report is 1563 commits behind head on main.

Files with missing lines	Patch %	Lines
.../lib/src/navigation/sentry_navigator_observer.dart	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #615      +/-   ##
==========================================
+ Coverage   90.05%   90.21%   +0.16%     
==========================================
  Files          85       92       +7     
  Lines        2755     3016     +261     
==========================================
+ Hits         2481     2721     +240     
- Misses        274      295      +21     

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[marandaneto]

left a comment other than that, LGTM