Kucoin connector update

Update Kucoin connector to include all the latest components and improvements to make it compliant with the connector standards (Binance connector as mentioned in the documentation). The changes introduced are:

• Refactor connector to make it a pure Python connector.
• Adapt all REST API interactions to use the recently developed web assistant.
• Adapt all websocket API interactions to use the recently developed web assistant.
• Change implementation of all data source classes to use only one websocket connection in each of them.
• Ensure all consumptions of the API are regulated by the use of the throttler (both REST and websocket API)
• Refactor the connector to use the newly developed client order tracker to manage in flight orders.
• Refactor the connector to stop using ad hoc logic to translate from exchange token-pair notation to client token-pair notation and the other way round. Instead keep track of the mapping base on the information provided by the exchange and the tokens composing each pair.
• Dosctrings for the public methods.
• Ensure we are using the latest version of the exchange API.
• Enable domains in Kucoin connector to allow the use of its testnet (officially called sandbox).

PR: https://github.com/hummingbot/hummingbot/pull/5197