[Enhancement] Optimize the gradle build script

### 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

Right now, we use gradle as the build tool. We create the distribution by copy the jar to target directory, this is not a good way, maybe we can use the assembly/distribution plugin to do this work like maven. I am not sure if gradle has this plugin.

### Describe the solution you'd like

Use assembly plugin to create the distribution.

### Are you willing to submit PR?

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

Start by locating the Gradle build script and the current distribution step that copies the jar into a target directory. Check Gradle's assembly or distribution plugin documentation and compare it with the existing build flow. Done means the distribution is created through the plugin rather than manual jar copying, with the existing build output still usable.

Written by the indexing model from the issue text.