OPCA capital gain distribution activities on activity event streams

Broker API

Adds a new OpcaCGDActivityV2 schema for OPCA capital gain distribution (CGD) transactions and includes it in the ActivityV2DetailNTA oneOf.

• Non-trade activity (NTA) events can now carry OPCA CGD detail payloads.
• The payload includes cusip and symbol for the affected security, matching sibling OPCA activity schemas.

Affected Endpoints

• GET /v2beta1/events/activities
• GET /v2beta1/accounts/{account_id}/events/activities/{event_id}