2.0.2

1.unify service discovery logic for dashboard and client
2.support registration server to multiple registration centers
3.actively clear registration information when the server is shut down
4.support configuring the maximum number of retries and maximum retry traffic for each domain
5.support setting delayed cancelation based on exception type.
6.add id field to uniquely identify transaction, used during updates and deletes.
7.use a separate thread pool to handle clients' REGISTER commands to avoid block other commands
8.optimize alarm threshold configuration
9.optimize channel select strategic during recovery