- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] I have checked the [FAQ](https://github.com/apache/dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 3.0.0


### Steps to reproduce this issue

1. dubbo config-center 相关yml配置如下
```
dubbo:
  ...
  config-center:
    address: nacos://xxxx:8848
    username: someusername
    password: xxxx
```

2. 在执行 org.apache.dubbo.config.bootstrap.DubboBootstrap#startConfigCenter 方法时会调用 configCenterConfig.refresh(); 方法。
3. setAddress方法，会覆盖已经设置过的username和password

```
public void setAddress(String address) {
        this.address = address;
        if (address != null) {
            try {
                URL url = URL.valueOf(address);
                setUsername(url.getUsername());
                setPassword(url.getPassword());
                updateIdIfAbsent(url.getProtocol());
                updateProtocolIfAbsent(url.getProtocol());
                updatePortIfAbsent(url.getPort());
                updateParameters(url.getParameters());
            } catch (Exception ignored) {
            }
        }
    }
```

### Expected Result

希望设置前先判断是否已经设置过相关属性值



import org.apache.dubbo.common.URL;
import org.apache.dubbo.common.constants.CommonConstants;
import org.apache.dubbo.common.utils.CollectionUtils;
import org.apache.dubbo.common.utils.StringUtils;
import org.apache.dubbo.common.utils.UrlUtils;
import org.apache.dubbo.config.support.Parameter;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicBoolean;
import static org.apache.dubbo.common.constants.CommonConstants.ANYHOST_VALUE;
import static org.apache.dubbo.common.constants.CommonConstants.CONFIG_CONFIGFILE_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.CONFIG_ENABLE_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.PATH_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.PROTOCOL_KEY;
import static org.apache.dubbo.config.Constants.CONFIG_APP_CONFIGFILE_KEY;
import static org.apache.dubbo.config.Constants.ZOOKEEPER_PROTOCOL;
/**
 * ConfigCenterConfig
 */
public class ConfigCenterConfig extends AbstractConfig {
    private AtomicBoolean inited = new AtomicBoolean(false);
    private String protocol;
    private String address;
    private Integer port;
    
    private String cluster;
    /* The namespace of the config center, generally it's used for multi-tenant,
    but it's real meaning depends on the actual Config Center you use.
    */
    private String namespace;