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.

ファイルやテストは指定されていません。まず MultiplayerService.Instance.CreateOrJoinSessionAsync と NetworkManager の接続フローを追跡し、キャンセルトークンをどこまで伝播させる必要があるかを把握します。ユーザーが MultiplayerService の関数を通じて進行中のセッション参加をキャンセルでき、パッケージ自体を変更する必要がなければ完了です。