Added log to show which URL is blocked by CORS. (#26347)

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/api4/websocket.go

@@ -32,7 +32,10 @@ func connectWebSocket(c *Context, w http.ResponseWriter, r *http.Request) {
 
 	ws, err := upgrader.Upgrade(w, r, nil)
 	if err != nil {
-		c.Err = model.NewAppError("connect", "api.web_socket.connect.upgrade.app_error", nil, err.Error(), http.StatusBadRequest)
+		params := map[string]any{
+			"BlockedOrigin": r.Header.Get("Origin"),
+		}
+		c.Err = model.NewAppError("connect", "api.web_socket.connect.upgrade.app_error", params, err.Error(), http.StatusBadRequest)
 		return
 	}