Error responses documented on portfolio history endpoints

The Get Account Portfolio History operations now document their error responses. Behavior is unchanged; only the API description is more complete.

• Adds a PortfolioHistoryError schema (titled "Portfolio History Error") used by the documented error responses.
• Documents the Deprecated-Params response header.

Broker API

Documented status codes: 401, 403, 404, 422, 429, 500, and 504.

Affected Endpoints

• GET /v1/trading/accounts/{account_id}/account/portfolio/history

Trading API

Documented status codes: 400, 403, 404, 422, 429, 500, and 504.

Affected Endpoints

• GET /v2/account/portfolio/history