Added function to automatically change rpc node to default

[HappyBerrysBoy]

• Added function to change to Default RPC URL
• If there is an error in the selected RPC Node, change to Default RPC URL

[melodyzxd]

这是来自QQ邮箱的假期自动回复邮件。你好，我最近正在休假中，无法亲自回复你的邮件。我将在假期结束后，尽快给你回复。