Needs example for simulcast

[jinleileiking]

I found this example:

https://github.com/pion/webrtc/tree/master/examples/simulcast

But this does not for poin generating simulcasting.

from test:

webrtc/peerconnection_media_test.go

Line 1216 in 2ffab96

func TestPeerConnection_Simulcast(t *testing.T) {

got some clue. but using this code is too bad.

Need more elegant codes.

[jinleileiking]

Need api like:

https://github.com/livekit/server-sdk-go/blob/34cd02a152ec8a695274a4c089348f803fbc73ed/localsampletrack.go#LL265C21-L265C21