What would you like to be added:
Layotto actuator API is designed as a collection of features to help users monitor and manage Layotto and applications during runtime,like health checking,metadata query and metrics query.
However,there is already a metrics api in MOSN,which means Layotto users have to configurate TWO http api in the configuration file: one for Layotto actuator API and one for MOSN metrics API.
We want to make it simpler for users. By adding a Layotto actuator metrics API,users can query metrics data including MOSN metrics and Layotto metrics.

Tasks included:

• add a Layotto actuator metrics API
• Layotto actuator metrics API can query MOSN metrics data

chinese:
任务：设计实现actuator metrics API，用于统计、展示metrics指标
背景：
Layotto Actuator API被设计用来提供一系列功能、帮助用户在运行时监控、管理应用，包括健康检查，元数据查询，metrics数据查询等功能。
然而，MOSN里也有个metrics API，这就意味着用户得配两个http端口，一个用来跑Layotto actuator API，一个用于MOSN metrics API。不仅配置麻烦，运维、使用API也麻烦。
我们希望让用户用起来更简单，只需要开一个端口。我们可以加个actuator metrics API，这个API既能查到Layotto metrics数据又能查到MOSN metrics数据。

要做的事情包括：

• 加个Layotto Actuator metrics API
• 这个API能查MOSN metrics数据

参考资料：
MOSN metrics

Why is this needed:
Make it simpler for users to configurate and monitor Layotto during runtime.