Improve OKEX integration

[darrylsite]

• Add the DEMO context for websocket
• Add the REST endpoing for ALgo order

[pimpcapital]

could you split it to 2 PRs?
I am not sure about demo context. I need to look into the use case.

[darrylsite]

Hi @freelunchcap,
I sure can split it in two MR.
The demo mode is to trade in the simulation mode. You can find the documentation at: https://www.okx.com/docs-v5/en/#overview-api-resources-and-support

Demo Trading Services
At present, the V5 API works for Demo Trading and users can request all APIs except the withdrawal, deposit and purchase/redemption endpoints.

The Demo Trading URL:

REST: https://www.okx.com
Public WebSocket：wss://wspap.okx.com:8443/ws/v5/public?brokerId=9999
Private WebSocket：wss://wspap.okx.com:8443/ws/v5/private?brokerId=9999
OKX account can be used for login on Demo Trading. If you already have an OKX account, you can log in directly.

Start API Demo Trading by the following steps:
Login OKX —> Assets —> Start Demo Trading —> Personal Center —> Demo Trading API -> Create Demo Trading V5 APIKey —> Start your Demo Trading