Override `_order_id_generator` field of the `OrderFactory` class

[sh7ning]

Is it possible to provide a method to override the _order_id_generator field of the OrderFactory class, without using the implementation of the ClientOrderIdGenerator class? Many exchanges have their own rules, such as gates need start with "t-", and some exchanges requiring numbers. I don't want to directly set the client_order_id parameter to the order, because I want to rely on the framework to check the uniqueness of client_order_id through caching.