Ftr: Add config loader hooks for 1.5

[ChangedenCZD]

Hook触发流程图

• 目前定义了9种类型的钩子，消费者4个，提供者4个，程序正常退出前1个
• 开发者可在config.Load前创建并添加钩子AddLoaderHooks
• 每种类型的钩子可创建和添加多个实例，在流程中对应类型的所有钩子都会被触发
• 所有消费者实例被验证前会触发beforeConsumerConnectHook
• 当消费者验证失败时，会触发consumerConnectFailHook
• 当消费者验证通过时，会触发consumerConnectSuccessHook
• 所有提供者实例被验证前会触发beforeProviderConnectHook
• 当提供者注册失败时，会触发consumerProviderFailHook
• 当提供者注册通过时，会触发consumerProviderSuccessHook
• 当allConsumersConnectCompleteHook被触发时，表示所有消费者已完成验证（即可调用）
• 当allProvidersConnectCompleteHook被触发时，表示所有提供者已完成注册（即可被调用）
• 当beforeShutDownHook被触发时，表示程序将要退出（panic的不会触发该钩子）

What this PR does:

func TestLoadWithLoaderHooks(t *testing.T) {
	extension.SetFilter(constant.GracefulShutdownConsumerFilterKey, func() filter.Filter {
		return &mockGracefulShutdownFilter{}
	})
	extension.SetFilter(constant.GracefulShutdownProviderFilterKey, func() filter.Filter {
		return &mockGracefulShutdownFilter{}
	})

	doInitConsumer()
	doInitProvider()

	ms := &MockService{}
	SetConsumerService(ms)
	SetProviderService(ms)

	extension.SetProtocol("registry", GetProtocol)
	extension.SetCluster(constant.ZONEAWARE_CLUSTER_NAME, cluster_impl.NewZoneAwareCluster)
	extension.SetProxyFactory("default", proxy_factory.NewDefaultProxyFactory)
	GetApplicationConfig().MetadataType = "mock"
	var mm *mockMetadataService
	extension.SetLocalMetadataService("mock", func() (metadataService service.MetadataService, err error) {
		if mm == nil {
			mm = &mockMetadataService{
				exportedServiceURLs: new(sync.Map),
				lock:                new(sync.RWMutex),
			}
		}
		return mm, nil
	})

	// create consumer loader hooks
	beforeConsumerConnectHook := NewBeforeConsumerConnectHook(func(info *ConsumerConnectInfo) {
		logger.Debug("BeforeConsumerConnectHook", info)
		assert.NotNil(t, info)
	})
	consumerConnectSuccessHook := NewConsumerConnectSuccessHook(func(info *ConsumerConnectInfo) {
		logger.Debug("ConsumerConnectSuccessHook", info)
		assert.NotNil(t, info)
	})
	consumerConnectFailHook := NewConsumerConnectFailHook(func(info *ConsumerConnectFailInfo) {
		logger.Debug("ConsumerConnectFailHook", info)
		assert.NotNil(t, info)
	})
	allConsumersConnectCompleteHook := NewAllConsumersConnectCompleteHook(func() {
		logger.Debug("AllConsumersConnectCompleteHook")
		RemoveLoaderHooks( // Remove some consumer loader hooks
			beforeConsumerConnectHook,
			consumerConnectSuccessHook,
			consumerConnectFailHook,
		)
		logger.Debug("LoaderHooks length = ", len(loaderHooks), " after AllConsumersConnectCompleteHook")
		// beforeConsumerConnectHook, consumerConnectSuccessHook 
                // and consumerConnectFailHook have been removed
		assert.Equal(t, len(loaderHooks), 6)
	})
	// create provider loader hooks
	beforeProviderConnectHook := NewBeforeProviderConnectHook(func(info *ProviderConnectInfo) {
		logger.Debug("BeforeProviderConnectHook", info)
		assert.NotNil(t, info)
	})
	providerConnectSuccessHook := NewProviderConnectSuccessHook(func(info *ProviderConnectInfo) {
		logger.Debug("ProviderConnectSuccessHook", info)
		assert.NotNil(t, info)
	})
	providerConnectFailHook := NewProviderConnectFailHook(func(info *ProviderConnectFailInfo) {
		logger.Debug("ProviderConnectFailHook", info)
		assert.NotNil(t, info)
	})
	allProvidersConnectCompleteHook := NewAllProvidersConnectCompleteHook(func() {
		logger.Debug("AllProvidersConnectCompleteHook")
		RemoveLoaderHooks( // Remove some provider loader hooks
			beforeProviderConnectHook,
			providerConnectSuccessHook,
			providerConnectFailHook,
		)
		logger.Debug("LoaderHooks length = ", len(loaderHooks), " after AllProvidersConnectCompleteHook")
		// beforeProviderConnectHook, providerConnectSuccessHook
                // and providerConnectFailHook have been removed
		assert.Equal(t, len(loaderHooks), 3)
	})

	beforeShutdownHook := NewBeforeShutdownHook(func() {
		logger.Debug("BeforeShutDownHook")
		RemoveLoaderHooks( // Remove some consumer and provider loader hooks
			// Consumer Hooks
			beforeConsumerConnectHook,
			consumerConnectSuccessHook,
			consumerConnectFailHook,
			allConsumersConnectCompleteHook,
			// Provider Hooks
			beforeProviderConnectHook,
			providerConnectSuccessHook,
			providerConnectFailHook,
			allProvidersConnectCompleteHook,
		)
		assert.Equal(t, len(loaderHooks), 1)
	})
	// add loader hooks before config.Load
	AddLoaderHooks(
		// Consumer Hooks
		beforeConsumerConnectHook,
		consumerConnectSuccessHook,
		consumerConnectFailHook,
		allConsumersConnectCompleteHook,
		// Provider Hooks
		beforeProviderConnectHook,
		providerConnectSuccessHook,
		providerConnectFailHook,
		allProvidersConnectCompleteHook,
		// Shut Down hook
		beforeShutdownHook,
	)
	// check loaderHooks length
	assert.Equal(t, len(loaderHooks), 9)

	Load()

	assert.Equal(t, ms, GetRPCService(ms.Reference()))
	ms2 := &struct {
		MockService
	}{}
	RPCService(ms2)
	assert.NotEqual(t, ms2, GetRPCService(ms2.Reference()))

	conServices = map[string]common.RPCService{}
	proServices = map[string]common.RPCService{}
	err := common.ServiceMap.UnRegister("com.MockService", "mock",
		common.ServiceKey("com.MockService", "huadong_idc", "1.0.0"))
	assert.Nil(t, err)
	consumerConfig = nil
	providerConfig = nil
}

Which issue(s) this PR fixes:

Fixes #1364

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

None

[ChangedenCZD]

使用事件分发机制实现 #1405

[ChangedenCZD]

@wangxw666 1.5版本的已改为 #1405 这个解决方案，3.0的建议废除原有的分发机制，改为Hook

[codecov-commenter]

Codecov Report

Merging #1372 (b5ab3be) into 1.5 (467c867) will decrease coverage by 2.34%.
The diff coverage is 68.88%.

@@            Coverage Diff             @@
##              1.5    #1372      +/-   ##
==========================================
- Coverage   58.07%   55.72%   -2.35%     
==========================================
  Files         275      277       +2     
  Lines       13381    16119    +2738     
==========================================
+ Hits         7771     8983    +1212     
- Misses       4650     6197    +1547     
+ Partials      960      939      -21     

Impacted Files	Coverage Δ
config/graceful_shutdown.go	57.30% <0.00%> (+3.01%)	⬆️
config/provider_config.go	62.06% <0.00%> (+7.52%)	⬆️
config/reference_config.go	80.00% <0.00%> (-1.67%)	⬇️
config_center/nacos/facade.go	62.50% <0.00%> (-27.16%)	⬇️
registry/consul/registry.go	51.64% <0.00%> (+2.31%)	⬆️
...gistry/event/protocol_ports_metadata_customizer.go	65.78% <ø> (+6.41%)	⬆️
registry/kubernetes/registry.go	64.15% <0.00%> (+13.03%)	⬆️
registry/zookeeper/listener.go	26.58% <0.00%> (-42.65%)	⬇️
remoting/etcdv3/client.go	55.69% <0.00%> (+2.69%)	⬆️
remoting/etcdv3/facade.go	0.00% <0.00%> (ø)
... and 311 more

---

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