Changes to Get All Subaccount Balances

removed the optional property service from the response with the 401 status

removed the optional property service from the response with the 500 status

added the required property subaccount_balances/items/exchange_index to the response with the 200 status

the subaccount_balances/items/balance response's property type changed from integer to string, and format from int64 to no format for status 200

endpoint added