[Feature] Add SubscriptionHandler admin endpoint

### Search before asking

- [X] I had searched in the [issues](https://github.com/apache/eventmesh/issues?q=is%3Aissue) and found no similar issues.

### Feature Request

Add `SubscriptionHandler` class at `org.apache.eventmesh.runtime.admin.handler.v2` package.

Provide client information for the current Runtime instance to EventMesh Dashboard. including:

- Information such as ip address, consumerGroup, etc. of the clients (specifically business applications using the SDK) and connectors on the source and sink side.
- Information about the topic that the Runtime is responsible for, etc.

You can refer to the infos reported to the registry at `org.apache.eventmesh.meta.nacos.service.NacosMetaService#updateMetaData`.

You may need to extend `org.apache.eventmesh.runtime.core.protocol.producer.ProducerManager` and record infos of source side.

Related issue (outdated): https://github.com/apache/eventmesh/issues/4400

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct) *

Start by reading org.apache.eventmesh.runtime.admin.handler.v2 and the existing NacosMetaService#updateMetaData flow, then inspect ProducerManager for how source-side information is tracked. Done means a SubscriptionHandler admin endpoint provides the Runtime's client, connector, topic, consumerGroup, and related information to the EventMesh Dashboard.

Written by the indexing model from the issue text.