This version mainly uses gRPC to replace HTTP as the communication between client and server. And refactor the data model of naming module to adapt new communication model.

Feature/Enhancement/Refactor

[#3328] nacos support grpc ,base functions submit. [#3334] Nacos config support gRPC. [#3343] Add naming support gRPC for register and deregister instance. [#3344] support config query in rpc channel ,add switch http/rpc at client side. [#3350] add server side connection listener ,and add client version. [#3352] Add naming support gRPC for query instance list and service info. [#3357] response model optimize area/Config kind/feature. [#3365] client reconnection optimize . [#3367]client reconnect optimize, combine first time start and reconnect code. [#3373] Naming support un/subscribe service by grpc. [#3385] server side client connection listener optimize and listen context and notifier updated. [#3386] Refactor for naming sdk. [#3478][#3521] Add gprc support-> add server push ack. [#3795][#3809][#3825][#3849][#3860] Adapt old client for naming module. [#4099][#4260][#4279][#4354][#4367] Add metadata for service and use raft to consistence. [#4383] Upgrade Nacos Api/Client modules to support JDK 1.8 compilation

There are many changes for this new feature. detail see https://github.com/alibaba/nacos/milestone/22?closed=1.