[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!

Inizia riproducendo la configurazione con l’immagine Docker standalone apache/iotdb e ispeziona /iotdb/conf/iotdb-system.properties, il log di avvio e l’output di runtime di enableAuditLog. Traccia come enable_audit_log viene caricato nella configurazione di runtime, quindi verifica che enableAuditLog diventi true e che /iotdb/logs/log_datanode_audit.log registri gli eventi di audit.

Scritto dal modello di indicizzazione a partire dal testo della issue.