Dubbo Admin multi-environment support

[AlbumenJ]

At present, an instance of Dubbo Admin can only connect to one set of environments (specified registry, namespace, group), and hope that one instance can connect to multiple sets of environments. Reference: https://www.yuque.com/docs/share/9fac3ccb-c0b9-41e8-bb43-2146b31db4c8

Project requirements:

• Pre-configure multiple environments through configuration, and can switch in the Admin interface
• Dubbo Admin only processes services in the current specified environment

Skills requirement:

• Proficiency in Java
• Proficiency in the use of relevant front-end technology

目前一个 Dubbo Admin 实例只能连接一套环境（指定的注册中心，namespace，group），希望一个实例能连接多套环境。 参考：https://www.yuque.com/docs/share/9fac3ccb-c0b9-41e8-bb43-2146b31db4c8

产出要求：

• 通过配制的方式预配制多套环境,并能在 Admin 界面中切换
• Dubbo Admin 只处理当前指定环境中的服务

技术要求：

• 熟练使用 Java
• 熟练使用相关前端技术