[FSSDK-12546] prepare for release flutter-sdk v3.5.0

Author: jaeopt

CHANGELOG.md

@@ -1,5 +1,14 @@
 # Optimizely Flutter SDK Changelog
 
+## 3.5.0
+May 4, 2026
+
+### New Features
+
+**Feature Rollout**: Added support for Feature Rollouts, a new experiment type combining Targeted Delivery simplicity with A/B test measurement capabilities. Feature Rollouts enable progressive rollouts with full impact analytics, metric tracking, and confidence intervals. See [Feature Rollout docs](https://support.optimizely.com/hc/en-us/articles/45552846481037-Run-Feature-Rollouts-in-Feature-Experimentation) for more information.
+
+---
+
 ## 3.4.3
 May 01, 2026