PLT-3711: Add websocket event for emoji addition (#6211)

* PLT-3711: Add websocket event for emoji addition

* (SA) updated as per review

This PR is edited directly to merge into master.

* (SA) updated as per review

This PR is edited directly to merge into master.

model/websocket_message.go

@@ -36,6 +36,7 @@ const (
 	WEBSOCKET_EVENT_REACTION_ADDED      = "reaction_added"
 	WEBSOCKET_EVENT_REACTION_REMOVED    = "reaction_removed"
 	WEBSOCKET_EVENT_RESPONSE            = "response"
+	WEBSOCKET_EVENT_EMOJI_ADDED         = "emoji_added"
 )
 
 type WebSocketMessage interface {