FPixelStreamingSetSessionDescriptionObserver

[FPixelStreamingSetSessionDescriptionObserver](API\Plugins\PixelStreaming\FPixelStreamingSetSessionDescrip-) WebRTC requires an implementation of `webrtc::SetSessionDescriptionObserver_ interface as a callback for setting session description, either on receiving remote `offer_ (`PeerConnection::SetRemoteDescription_) of on sending `answer_ (`PeerConnection::SetLocalDescription_)