Added ROOM_CLOSED as a DisconnectReason (#778)

* Added ROOM_CLOSED as a DisconnectReason

When all independent participants leave the room, the room would close
and disconnect all dependent participants. They should receive the correct
reason. Currently we are sending `UNKNOWN_REASON`

* generated protobuf

* changeset

---------

Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

.changeset/unlucky-parrots-raise.md

@@ -0,0 +1,6 @@
+---
+"github.com/livekit/protocol": patch
+"@livekit/protocol": patch
+---
+
+Added RoomClosed as a DisconnectReason

protobufs/livekit_models.proto

@@ -373,15 +373,26 @@ message DisabledCodecs {
 
 enum DisconnectReason {
   UNKNOWN_REASON = 0;
+  // the client initiated the disconnect
   CLIENT_INITIATED = 1;
+  // another participant with the same identity has joined the room
   DUPLICATE_IDENTITY = 2;
+  // the server instance is shutting down
   SERVER_SHUTDOWN = 3;
+  // RoomService.RemoveParticipant was called
   PARTICIPANT_REMOVED = 4;
+  // RoomService.DeleteRoom was called
   ROOM_DELETED = 5;
+  // the client is attempting to resume a session, but server is not aware of it
   STATE_MISMATCH = 6;
+  // client was unable to connect fully
   JOIN_FAILURE = 7;
+  // Cloud-only, the server requested Participant to migrate the connection elsewhere
   MIGRATION = 8;
+  // the signal websocket was closed unexpectedly
   SIGNAL_CLOSE = 9;
+  // the room was closed, due to all Standard and Ingress participants having left
+  ROOM_CLOSED = 10;
 }
 
 message RTPDrift {