accept publisher sdp and return optimal publish code, remove tmp preferredCodec (#829)

Author: thesyncim

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

@@ -165,6 +165,7 @@ message JoinRequest {
   string session_id = 2;
   // dumb SDP that allow us to extract subscriber's decode codecs
   string subscriber_sdp = 3;
+  string publisher_sdp = 8;
   models.ClientDetails client_details = 4;
   // Deprecated: use ReconnectDetails instead
   Migration migration = 5 [deprecated = true];
@@ -202,6 +203,7 @@ message JoinResponse {
   models.CallState call_state = 1;
   bool reconnected = 2;
   int32 fast_reconnect_deadline_seconds = 3;
+  models.Codec publish_codec = 4;
 }
 
 // ParticipantJoined is fired when a user joins a call