2.0.0-ALPHA.1 (Dec 5th, 2020)

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.