MacOS安装cocoapods-国内加速版本

在安装Flutter时，提示未安装cocoa pods。如果直接安装，下载的速度非常慢，则需要根据gem的源地址。

错误如下:

#flutter doctor 
[!] Xcode - develop for iOS and macOS (Xcode 15.4)
    ✗ Unable to get list of installed Simulator runtimes.
    ✗ CocoaPods not installed.
        CocoaPods is used to retrieve the iOS and macOS platform side's plugin code that responds to your plugin usage on the Dart side.
        Without CocoaPods, plugins will not work on iOS or macOS.
        For more info, see https://flutter.dev/platform-plugins
      To install see https://guides.cocoapods.or