HackWeek - Feature Flags Support

[marandaneto]

📜 Description

This PR adds Feature Flags Support for the Dart/Flutter SDK.
This is a HackWeek project only.
Spec https://github.com/getsentry/hackweek-feature-flags

#skip-changelog

💡 Motivation and Context

💚 How did you test it?

📝 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

Merging #984 (163ddcf) into main (c76b7ca) will increase coverage by 1.59%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #984      +/-   ##
==========================================
+ Coverage   89.55%   91.14%   +1.59%     
==========================================
  Files         106        9      -97     
  Lines        3322      192    -3130     
==========================================
- Hits         2975      175    -2800     
+ Misses        347       17     -330     

Impacted Files	Coverage Δ
dart/lib/src/default_integrations.dart
dart/lib/src/hub.dart
dart/lib/src/hub_adapter.dart
dart/lib/src/noop_hub.dart
dart/lib/src/protocol/dsn.dart
dart/lib/src/sentry.dart
dart/lib/src/sentry_client.dart
dart/lib/src/sentry_options.dart
dart/lib/src/sentry_traces_sampler.dart
dart/lib/src/transport/http_transport.dart
... and 87 more

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[getsantry]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you remove the label Waiting for: Community, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀