Support cancelling MultiplayerService session joining functions

Is your feature request related to a problem? Please describe.
It takes several seconds to join a session through MultiplayerService. I'd like to let users cancel a connection attempt during the connection process.

Describe the solution you'd like
I'd like to pass cancellation tokens to functions like MultiplayerService.Instance.CreateOrJoinSessionAsync.

Describe alternatives you've considered
I've tried preventing the NetworkManager from connecting to a session if my own connection function wrapping MultiplayerService.Instance.CreateOrJoinSessionAsync is cancelled, but I cannot find a clean way to do this. I have also considered modifying the Unity.Services.Multiplayer package myself, but I would rather not do this.

未指定任何文件或测试。首先跟踪 MultiplayerService.Instance.CreateOrJoinSessionAsync 和 NetworkManager 的连接流程，以了解需要在哪里传递取消令牌。完成标准是：用户可以通过 MultiplayerService 的函数取消正在进行的会话加入，而无需自行修改该包。