**app/models/operations/feature_flags/strategy.rb:**

Adds support for flexibleRollout strategy.

**ee/changelogs/unreleased/feature-flags-rollout-session-random.yml:**

Changelog.

**ee/app/controllers/projects/feature_flags_controller.rb:**

Updates to support permitted parameters for flexibleRollout.

**ee/spec/controllers/projects/feature_flags_controller_spec.rb:**

Tests for the controller to support flexibleRollout.

**ee/spec/requests/api/feature_flags_spec.rb:**

Tests for the API to support flexibleRollout.

**spec/models/operations/feature_flags/strategy_spec.rb:**

Tests for the model to support flexibleRollout.

**doc/api/feature_flags.md:**

Documentation for the new API support.