feat(config): Optimize configuration file loading logic

[NewFuture]

Enhance the logic for loading configuration files, including improved error handling and automatic generation of default configuration files when necessary. Additionally, add favicon support to the configuration.

默认配置文件 #117

1. 当前目录 config.json
2. 用户目录 ~/.ddns/config.json
3. 系统目录 /etc/ddns/config.json