问题描述：发现服务关停过程中未正常调用ServiceDiscovery的unregister方法

问题原因：
1. preDestroy中，先执行destroyRegistries()，再执行destroyServiceDiscoveries()，最后执行unregisterServiceInstance()
~~~
    @Override
    public void preDestroy() {
        synchronized (destroyLock) {
            if (isStopping() || isStopped()) {
                return;
            }
            onStopping();

            destroyRegistries();
            destroyServiceDiscoveries();
            destroyMetadataReports();

            unRegisterShutdownHook();
            if (asyncMetadataFuture != null) {
                asyncMetadataFuture.cancel(true);
            }
            unregisterServiceInstance();
        }
    }
~~~
2. destroyRegistries()方法中调用destroyAll()方法，将容器registries中所有Registry进行销毁并从容器registries中移除，此时容器registries中已经没有数据，并且所有与注册中心的通信工具（如nacos的NamingService，zk的CuratorFramework）都被销毁
~~~
   public void destroyAll() {
        if (!destroyed.compareAndSet(false, true)) {
            return;
        }

        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Close all registries " + getRegistries());
        }
        // Lock up the registry shutdown process
        lock.lock();
        try {
            for (Registry registry : getRegistries()) {
                try {
                    registry.destroy();
                } catch (Throwable e) {
                    LOGGER.warn(e.getMessage(), e);
                }
            }
            registries.clear();
        } finally {
            // Release the lock
            lock.unlock();
        }
    }
~~~
3. destroyServiceDiscoveries()、unregisterServiceInstance()执行时，已经无法从容器registries中获取ServiceDiscoveries（即使能获取到，与注册中心的通信工具NamingService\CuratorFramework等已经被销毁无法使用）

修改方法：将unregisterServiceInstance()调整到destroyRegistries()之前，并删除destroyServiceDiscoveries()
~~~
   @Override
    public void preDestroy() {
        synchronized (destroyLock) {
            if (isStopping() || isStopped()) {
                return;
            }
            onStopping();
            
            unregisterServiceInstance();
            destroyRegistries();
            destroyMetadataReports();

            unRegisterShutdownHook();
            if (asyncMetadataFuture != null) {
                asyncMetadataFuture.cancel(true);
            }

        }
    }
~~~

if (isNotEmpty(appGroup)) {
                    appConfigContent = dynamicConfiguration.getProperties
                        (isNotEmpty(configCenter.getAppConfigFile()) ? configCenter.getAppConfigFile() : configCenter.getConfigFile(),
                            appGroup
                        );
                }
                try {
                    environment.updateExternalConfigMap(parseProperties(configContent));
                    environment.updateAppExternalConfigMap(parseProperties(appConfigContent));
                } catch (IOException e) {
                    throw new IllegalStateException("Failed to parse configurations from Config Center.", e);
                }
            }
            return dynamicConfiguration;
        }
        return null;
    }
    /**
     * Get the instance of {@link DynamicConfiguration} by the specified connection {@link URL} of config-center
     *
     * @param connectionURL of config-center
     * @return non-null
     * @since 2.7.5
     */
    private DynamicConfiguration getDynamicConfiguration(URL connectionURL) {
        String protocol = connectionURL.getProtocol();
        DynamicConfigurationFactory factory = ConfigurationUtils.getDynamicConfigurationFactory(applicationModel, protocol);
        return factory.getDynamicConfiguration(connectionURL);
    }
    private volatile boolean registered;