Add feature_enabled_by_namespace_ids to event definition schema
Problem
In #438827 (closed) we've added a new property to events (feature_enabled_by_namespace_ids).
In order to keep event definitions as the single source of truth we need to consider adding this field to the list of identifiers https://docs.gitlab.com/ee/development/internal_analytics/internal_event_instrumentation/event_definition_guide.html#example-event-definition
Conversation !148463 (comment 1845462867)
Desired Outcome
The new property is documented in event definitions