[RFC] Update API docs and specs

[thangnguyen-19]

Note

Introduces builder and isolated margin features, plus instrument and history schema updates across REST/WS docs.

• Adds builder and builder_fee to order schemas/responses/feeds; includes builder fee details on fills and new builder order reject reasons; documents ApiAuthorizeBuilderRequest, ApiAuthorizedBuilder, ApiGetAuthorizedBuildersResponse, and builder fill history (request/response/schema)
• Adds position margin management: PositionMarginType schema, margin fields on positions/sub-account (and WS feeds), ApiSetSubAccountPositionMarginConfig{Request,Response}, isolated margin add and limits APIs; marks set_initial_leverage as DEPRECATED
• Extends instrument schemas/responses with min_notional; updates instrument_display
• Enhances histories: fill responses include is_liquidation; funding payment history request gains kind, base, quote filters
• Propagates new builder-related reject reasons across order_state, order_reject_reason, cancel/order state feeds

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