Work on subscription with configurationmanagement

applications/rtdt-manager/gosdnutil/gosdnutil.go

applications/rtdt-manager/main.go

applications/rtdt-manager/rtdt-manager/rtdt-manager.go

applications/rtdt-manager/sdnconfig/sdnconfig.go

applications/rtdt-manager/test/downloaded-config.json

applications/rtdt-manager/test/main.go

controller/configs/gNMISubscriptions.txt.example

controller/northbound/server/configurationmanagement.go

controller/northbound/server/nbi.go

controller/northbound/server/networkElement.go

controller/nucleus/networkElement.go