Ftr: Added more event distribution types and improved event distribution mechanism for 1.5

[ChangedenCZD]

What this PR does:
分发机制

单元测试

// 实现事件分发接口
type CustomEvent struct {
	t *testing.T
}

// implements interfaces.ConfigPostProcessor's functions
func (c CustomEvent) PostProcessReferenceConfig(u *common.URL, event string, errMsg *string) {
	logger.Debug("PostProcessReferenceConfig Start")
	logger.Debug("Event: ", event)
	logger.Debug("Url: ", u)
	if errMsg != nil {
		logger.Debug("Error Message: ", *errMsg)
	}
	logger.Debug("PostProcessReferenceConfig End")
	assert.Equal(c.t, u.GetParam(constant.SIDE_KEY, ""), "consumer")
}
func (c CustomEvent) PostProcessServiceConfig(u *common.URL, event string, errMsg *string) {
	logger.Debug("PostProcessServiceConfig Start")
	logger.Debug("Event: ", event)
	logger.Debug("Url: ", u)
	if errMsg != nil {
		logger.Debug("Error Message: ", *errMsg)
	}
	logger.Debug("PostProcessServiceConfig End")
	assert.Equal(c.t, u.GetParam(constant.SIDE_KEY, ""), "provider")
}
func (c CustomEvent) AllReferencesConnectComplete() {
	logger.Debug("AllConsumersConnectComplete")
}
func (c CustomEvent) AllServicesListenComplete() {
	logger.Debug("AllServicesListenComplete")
}
func (c CustomEvent) BeforeShutdown() {
	logger.Debug("BeforeShutdown")
}

func TestLoadWithEventDispatch(t *testing.T) {
	doInitConsumer()
	doInitProvider()
	for _, v := range providerConfig.Services {
		v.export = true
	}

	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.SetMetadataService("mock", func() (metadataService service.MetadataService, err error) {
		if mm == nil {
			mm = &mockMetadataService{
				exportedServiceURLs: new(sync.Map),
				lock:                new(sync.RWMutex),
			}
		}
		return mm, nil
	})

	extension.SetConfigPostProcessor("TestLoadWithEventDispatch", CustomEvent{t})

	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:
钩子方式的实现方式 #1372

Does this PR introduce a user-facing change?:

- 需要重新实现interfaces.ConfigPostProcessor中的PostProcessReferenceConfig、PostProcessServiceConfig函数，参数从[u *common.URL]拓展为[u *common.URL, event string, errMsg *string]
- 额外实现interfaces.ConfigPostProcessor中的AllReferencesConnectComplete、AllServicesListenComplete、BeforeShutdown函数

[codecov-commenter]

Codecov Report

Merging #1405 (fa59c63) into 1.5 (467c867) will decrease coverage by 2.13%.
The diff coverage is 64.13%.

❗ Current head fa59c63 differs from pull request most recent head 460bcd2. Consider uploading reports for the commit 460bcd2 to get more accurate results

@@            Coverage Diff             @@
##              1.5    #1405      +/-   ##
==========================================
- Coverage   58.07%   55.94%   -2.14%     
==========================================
  Files         275      276       +1     
  Lines       13381    15981    +2600     
==========================================
+ Hits         7771     8940    +1169     
- Misses       4650     6094    +1444     
+ Partials      960      947      -13     

Impacted Files	Coverage Δ
common/extension/config_post_processor.go	0.00% <0.00%> (ø)
config/graceful_shutdown.go	55.43% <0.00%> (+1.14%)	⬆️
config/provider_config.go	62.06% <0.00%> (+7.52%)	⬆️
config_center/nacos/facade.go	71.87% <0.00%> (-17.79%)	⬇️
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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