DubboAdmin支持Dubbo3+Nacos做如下变更是否合适

[liudaac]

Environment

• Dubbo Admin version: 0.5.0
• Java version: 1.8
• Nacos: 2.1.0

Steps to reproduce this issue

1. 集成Dubbo3.x应用发现问题

NacosServiceMapping的初始化逻辑注入Url为metadataUrl，参考代码ConfigServer.getServiceMapping(ServiceDiscovery serviceDiscovery, InstanceRegistryCache instanceRegistryCache)
而目前按照Dubbo的处理逻辑，metadataUrl的group默认值为dubbo、registryUrl的group默认值为DEFAULT_GROUP，即存在metadataUrl与registryUrl不一致的情况，此时NacosServiceMapping使用metadataUrl初始化则导致getAllServiceNames()结果为空，现象为管理界面服务列表为空，此处应该修改为使用registryUrl进行初始化，才能使服务列表正常获取和显示，参考如下

@Bean
    @DependsOn("dubboRegistry")
    ServiceMapping getServiceMapping(ServiceDiscovery serviceDiscovery, InstanceRegistryCache instanceRegistryCache) {
        ServiceMapping serviceMapping = new NoOpServiceMapping();
        if (registryUrl == null) {
            return serviceMapping;
        }
        MappingListener mappingListener = new AdminMappingListener(serviceDiscovery, instanceRegistryCache);
        serviceMapping = ExtensionLoader.getExtensionLoader(ServiceMapping.class).getExtension(registryUrl.getProtocol());
        serviceMapping.addMappingListener(mappingListener);
        serviceMapping.init(registryUrl);
        return serviceMapping;
    }

[wuwen5]

#1148