[Enhancement] Implement 'NameResolver' and 'LoadBalancer' extension points on top of the Java SDK's protocol

### Search before asking

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

### Enhancement Request

Implement 'NameResolver' and 'LoadBalancer' extension points on top of the Java SDK's protocol. At present, the Java SDK lacks a unified load balancing extension, and only provides an optional load balancing implementation for the HTTP protocol (see org.apache.eventmesh.common.loadbalance.LoadBalanceSelector).

### Describe the solution you'd like

Implement 'NameResolver' and 'LoadBalancer' extension points on top of the Java SDK's protocol, support user-defined load balancing implementation.

### Are you willing to submit PR?

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

Start by examining the Java SDK protocol and the existing org.apache.eventmesh.common.loadbalance.LoadBalanceSelector used by the HTTP protocol. Determine how NameResolver and LoadBalancer should fit across the SDK protocols and how user-defined implementations are registered. Done means both extension points are available through the Java SDK with a consistent user-defined load-balancing path.

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