[Bug] `enable_audit_log` configuration not taking effect - always shows false despite correct setup

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/iotdb/issues) and found nothing similar.

### Version

- **Versions Tested**: 2.0.5, 2.0.4, 2.0.3, 1.3.4-1 (standalone mode)
- **Deployment**: Docker (apache/iotdb:*-standalone images)

### Describe the bug and provide the minimal reproduce step

1. Set configuration via environment variable or in `iotdb-system.properties`:
```yaml
environment:
- enable_audit_log=true
```

2. Check runtime configuration:
```bash
docker logs iotdb-service 2>&1 | grep -i "enableAuditLog"
```

### What did you expect to see?

**Expected:**
```
enableAuditLog=true;
```

### What did you see instead?

**Actual:**
```
enableAuditLog=false;
```

### Anything else?

1. Configuration file contains `enable_audit_log=true` correctly
2. Startup log shows: `append enable_audit_log=true /iotdb/conf/iotdb-system.properties`
3. But runtime always shows: `enableAuditLog=false;`
4. Audit log file `/iotdb/logs/log_datanode_audit.log` is created but remains empty

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

首先，使用独立的 Docker 镜像 apache/iotdb 重现该设置，并检查 /iotdb/conf/iotdb-system.properties、启动日志以及 enableAuditLog 的运行时输出。跟踪 enable_audit_log 如何加载到运行时配置中，然后验证 enableAuditLog 变为 true，并且 /iotdb/logs/log_datanode_audit.log 记录审计事件。

由索引模型根据 Issue 内容生成。