* Remove double write switch and upgrade from 1.X switch.
* Remove IFilterConfig.java
* Remove some deprecated constants and methods
* Remove some deprecated classes in nacos-core
* Remove some deprecated config
* Remove some deprecated codes in naming module
* Remove some deprecated codes in sys module
* Fix unit test
* Try to make UdpConnectorTest pass more easier.
* Check cluster name in server-side when register ephemeral instance
* Check cluster name in server-side when register persistent instance
* add unit test for register instance
* add unit test for NamingHttpClientProxy
* remove catching NacosException to throw NacosRuntimeException