[Bug] [Zeta] Java process does not receive SIGTERM when running SeaTunnel inside container

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/seatunnel/issues?q=is%3Aissue+label%3A%22bug%22) and found no similar issues.

### What happened

When running SeaTunnel inside a Docker/Kubernetes container, the Java process cannot gracefully shut down because it never receives the SIGTERM signal sent by the container runtime.
Currently, the startup script (bin/seatunnel-cluster.sh) launches Java like this (when not using -d):
``` bash
java ${JAVA_OPTS} -cp ${CLASS_PATH} ${APP_MAIN} ${args}
```

In this case:
• The shell script itself becomes PID 1 in the container.
• The Java process runs as a child process of the shell.
• When the container is stopped, SIGTERM is only delivered to the shell script (PID 1), not to the Java process.
• The script exits immediately without forwarding the signal, leaving Java as an orphan process.
• Finally, the Java process is killed by SIGKILL after the grace period, preventing SeaTunnel from shutting down gracefully.

This causes issues such as:
• Shutdown hooks in Java never being executed.
• Potential data loss or corruption when SeaTunnel tasks are abruptly killed.

### SeaTunnel Version

2.3.11

### SeaTunnel Config

```conf
none
```

### Running Command

```shell
./bin/seatunnel-cluster -r xxx
```

### Error Exception

```log
none
```

### Zeta or Flink or Spark Version

_No response_

### Java or Scala Version

_No response_

### Screenshots

_No response_

### Are you willing to submit PR?

- [x] 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)