Migrate legacy duo chat data from contributor to namespace filtering

Summary

Add the ability to toggle legacy duo chat data from contributor-based filtering to namespace-based filtering, following the same pattern used for other AI events.

Background

As part of the migration from contributions-based filtering to namespace path filtering (tracked in epic &19427), we need to update the legacy duo chat data endpoint to support namespace filtering.

Implementation

The functionality should be behind a feature flag, similar to what has been implemented for other events in this epic (e.g., use_ai_events_namespace_path_filter).

Acceptance Criteria

• Feature flag created to toggle between contributor and namespace filtering for legacy duo chat data
• Namespace filtering implementation added for legacy duo chat data
• Feature flag can be enabled/disabled without breaking existing functionality
• Implementation follows the same pattern as other migrated endpoints in this epic

Related

Parent epic: &19427