New symbol fields on options activity events

Broker API

Adds symbol, contract_symbol, and cusip to the CommonOptionsActivityV2 schema, so options activity events now identify the underlying and the specific contract.

• Adds the OPCSHActivityV2 schema for option cash settlement activities.
• Adds OPCSHActivityV2 to the activity detail variants returned by the activity event endpoints.

Affected Endpoints

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