"集群概览" 页面及相关接口详情

https://github.com/apache/dubbo-admin/issues/1140

Dubbo 集群接口：http://localhost:38080/api/dev/metrics/cluster
```json
{"data":{"all":0,"application":0,"consumers":0,"providers":0,"services":0}}
```

Dubbo 集群元数据接口：http://localhost:38080/api/dev/metrics/metadata
```json
{"versions":[],"configCenter":"127.0.0.1:2181","registry":"127.0.0.1:2181","metadataCenter":"127.0.0.1:2181","protocols":[],"rules":["DemoService:1.0.0:test.configurators","DemoService4:bb:aa.configurators","demo.tag-router","DemoService:11:aa.condition-router","demo.configurators","DemoService:22:aa.configurators","DemoService::.condition-router","DemoService1::.configurators","DemoService2::.configurators","demo2.tag-router","DemoService:test:1.0.0.configurators","DemoService::.configurators","DemoService2:v2:group2.configurators","DemoService:11:aa.configurators"]}
```

Dubbo 集群调用情况接口（后台依赖prometheus）：http://localhost:38080/api/dev/metrics/flow

Admin 进程环境信息接口：http://localhost:38080/api/dev/version
```json
{"gitVersion":"dubbo-admin-","gitCommit":"$Format:%H$","gitTreeState":"","buildDate":"1970-01-01T00:00:00Z","goVersion":"go1.20.4","compiler":"gc","platform":"darwin/arm64"}
```

Start by reading the linked issue #1140 and querying the listed /api/dev/metrics/cluster, /metadata, /flow, and /api/dev/version endpoints. Define the cluster overview page around the response fields shown here, including Prometheus-backed flow data; done means the page and its related interfaces present the required cluster, metadata, flow, and environment information.

Written by the indexing model from the issue text.