[Feature] Implment Counter in local cache

[robocanic]

What would you like to be added:

The homepage of Dubbo admin is full of different metrics, these metrics are statistical analysis attributes of different Resource. We need to defined a Counter to count the number of these metrics in cache in case to support the homepage data query.

Below are the procedures to implement homepage data query:

1. Define a unified CounterManager, which is responsible for managing different kinds of Counter.
2. Subscribe the specific type of Resource Event through Event Bus.
3. Create or update the number of Counter during event processing.
4. Implement http handler of the homepage data query

Why is this needed:
The query of homepage data includes different kinds of resources. In the last version of admin, we list all the objects to get the metric like the number of application. It's really cumbersome. So we need to improve it. For now, using event bus we can easily catch a resource event and calculate the metrics. And metrics do not need to be completely precise and it's perfect for implmenting Counter in the event process.

[WyRainBow]

plz give me

[robocanic]

The feature has been implemented, closed