[REQUEST] Add API to stop stream

[karasusan]

C# API is not provided for stopping video/audio streaming. There is no other way but to disconnect peers.

This is an original request in Unity forum. https://forum.unity.com/threads/unity-render-streaming-introduction-faq.742481/page-16#post-7508039

StreamSenderBase and StreamReceiverBase should provide method to stop stream. Or should implements OnEnable/OnDisable methods.

[karasusan]

memo: URS-161