Improve UI show/hide conditions

Problem 1

push_frontend_feature_flag(:generate_cube_query, project.namespace)

The feature flag is supposed to be project scoped, not namespace scoped. So we're currently requiring the FF to be enabled for both for the UI to show

Problem 2

This feature flag is the only thing checked for showing / hiding the new cube query generation UI. We should match the same conditions checked in the backend

Implementation plan

1. Update analytics_dashboards_list_app_data model to include a new cube_query_generation_enabled property which uses existing backend ::generate_cube_query_enabled value (combined FF and other checks)

2. Update frontend to use this property instead of checking the FF directly

3. Remove the push_frontend_feature_flag

4. Update tests