Add setEnabled function to RemoteTrackPublication like in other SDKs

[thedrhax14]

Other SDKs allow enabling and disabling tracks: https://docs.livekit.io/home/client/tracks/subscribe/#enabling-disabling-tracks. Identical functionality is needed in client-sdk-unity. Current SDK has only RemoteTrackPublication.SetSubscribed

[ladvoc]

The SetEnabled method has since been added to IRemoteTrack.