dubbo admin增加guest用户

最近出了一次故障，发现是dubbo admin的配置管理被修改了，连接的zookeeper集群地址写错，导致应用调用dubbo服务，连接了错误的zookeeper集群地址。
目前dubbo admin只有root权限的账号，而开发需要查看dubbo的连接信息，建议新增一个guest用户，用于只读。

No file, test, or entry point is named. Start by tracing Dubbo Admin's existing root authentication and configuration-management authorization, then identify the paths governing ZooKeeper connection visibility and edits. Done means a guest account can view connection information while being unable to modify configuration.

Written by the indexing model from the issue text.