[VID-1232] Add negotiation id for subscriber signaling offer-answer methods (#1717)

Author: brunoribc

protobuf/video/sfu/event/events.pb.go

@@ -242,6 +242,7 @@ message ParticipantUpdated {
 message SubscriberOffer {
   bool ice_restart = 1;
   string sdp = 2;
+  uint32 negotiation_id = 3;
 }
 
 message PublisherAnswer {

protobuf/video/sfu/event/events.proto

@@ -162,6 +162,7 @@ message SendAnswerRequest {
   stream.video.sfu.models.PeerType peer_type = 1;
   string sdp = 2;
   string session_id = 3;
+  uint32 negotiation_id = 4;
 }
 
 message SendAnswerResponse {