调整工具类的方法，优化方法调用及增加迁移工具及其用法

docs/storage.md

@@ -325,8 +325,20 @@ func main() {
     proxyHandler := storage.NewProxyHandler(ossStorage)
 
     // 创建中间件链
+    var corsConfig *middleware.CORSConfig
+    if cfg.GetCORS() != nil {
+        c := cfg.GetCORS()
+        corsConfig = middleware.NewCORSConfig(
+            c.AllowedOrigins,
+            c.AllowedMethods,
+            c.AllowedHeaders,
+            c.ExposedHeaders,
+            c.AllowCredentials,
+            c.MaxAge,
+        )
+    }
     chain := middleware.NewChain(
-        middleware.CORS(cfg.GetCORS()),
+        middleware.CORS(corsConfig),
         middleware.Timezone,
     )