Paper Trading - Test feature for trade_updates stream

**Is your feature request related to a problem? Please describe.**
I want to be able to test my script that listen to trade_updates through websocket. However, I would only receive events during actual market operating hours, which prevent me from testing outside of those hours.

**Describe the solution you'd like**
Have paper orders be simulated through a specific convention in a field (for e.g. `client_order_id`) that will determined whether the paper order will be immediately filled/rejected etc, even outside of market operating hours

**Describe alternatives you've considered**
There's no other way for me to achieve the above atm.