[Feature] Enhance the serverless ability of EventMesh

### 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

EventMesh currently has Eventing capabilities in the serverless field, but it should also improve and supplement the automatic expansion and contraction capabilities of eventmesh's own services and access services. This service is the coordinator responsible for automatically scaling services connected to EventMesh, supporting automatic scaling from 0 to n and scaling down from n to 0 based on event traffic or other user conditions.

Implement the auto scaling service for eventmesh, which can support different auto scaling strategies by default, or knative and keda can be selected as plugin services for automatic expansion and contraction of the service.

### 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) *

No files, tests, or entry points are named in the issue. First map EventMesh's existing serverless eventing and service-access components, then clarify the coordinator's scope, supported scaling conditions, default strategies, and plugin boundaries for Knative and KEDA before implementation can be considered complete.

Written by the indexing model from the issue text.