add metrics support in dubbo admin

[Minxuan Zhuang]

Hello Dubbo Community,
   I'd like to add metrics support in dubbo admin based on this[1],  when
it's done， we can check dubbo service metrics information on a single
server.


[1]
https://lists.apache.org/thread.html/d86bfc428a04451e01de5b9f9844822f65ab1944e102474caf6e0a3a@%3Cdev.dubbo.apache.org%3E