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);
            }

        }
    }
~~~

private void registerServiceInstance() {
        try {
            registered = true;
            ServiceInstanceMetadataUtils.registerMetadataAndInstance(applicationModel);
        } catch (Exception e) {
            logger.error("5-11", "configuration server disconnected", "", "Register instance error.", e);
        }
        if (registered) {
            
            asyncMetadataFuture = frameworkExecutorRepository.getSharedScheduledExecutor().scheduleWithFixedDelay(() -> {
                
                if (applicationModel.isDestroyed()) {
                    return;
                }
                try {
                    if (!applicationModel.isDestroyed() && registered) {
                        ServiceInstanceMetadataUtils.refreshMetadataAndInstance(applicationModel);
                    }
                } catch (Exception e) {
                    if (!applicationModel.isDestroyed()) {
                        logger.error("5-12", "", "", "Refresh instance and metadata error.", e);
                    }
                }
            }, 0, ConfigurationUtils.get(applicationModel, METADATA_PUBLISH_DELAY_KEY, DEFAULT_METADATA_PUBLISH_DELAY), TimeUnit.MILLISECONDS);
        }
    }
    private void unregisterServiceInstance() {
        if (registered) {
            ServiceInstanceMetadataUtils.unregisterMetadataAndInstance(applicationModel);
        }