【AUTH】抽象 ClientAuthService，支持自定义Auth逻辑

[catcherwong]

Describe what happened (or what feature you want)

对照下面的实现， 抽离Auth相关的逻辑，同时完成默认的用户名密码登陆逻辑，可以适配 nacos 服务端 Auth SPI 化。

https://github.com/alibaba/nacos/blob/develop/plugin/auth/src/main/java/com/alibaba/nacos/plugin/auth/spi/client/ClientAuthService.java

https://github.com/alibaba/nacos/blob/develop/client/src/main/java/com/alibaba/nacos/client/auth/impl/NacosClientAuthServiceImpl.java