Enable goimports linter

build/ci/.golangci-config/.golangci.yml

cli/capabilities.go

cli/get.go

cli/set.go

cli/subscribe.go

cli/target.go

cmd/util.go

database/client.go

nucleus/controller.go

nucleus/device_test.go

nucleus/gnmi_transport.go

nucleus/gnmi_transport_test.go

nucleus/http_test.go

nucleus/initialise_test.go

nucleus/pnd/change.go

nucleus/pnd/change_test.go

nucleus/pnd/initialise_test.go

nucleus/principalNetworkDomain.go

nucleus/principalNetworkDomain_test.go

nucleus/restconf_transport.go