Changes to List Capital Products digital funds

added the optional property error/authorization to the response with the default status

added the optional property data/items/sell_availability to the response with the 200 status

added the optional property data/items/availability to the response with the 200 status

added the optional property data/items/approval_category to the response with the 200 status

added the optional property error/api_client_id to the response with the default status