Update CLI commands to Notification API v1beta2

cmd/flux/alert.go

cmd/flux/alert_provider.go

cmd/flux/create_alert.go

cmd/flux/create_alertprovider.go

cmd/flux/create_receiver.go

cmd/flux/delete_alert.go

cmd/flux/delete_alertprovider.go

cmd/flux/delete_receiver.go

cmd/flux/export_alert.go

cmd/flux/export_alertprovider.go

cmd/flux/export_receiver.go

cmd/flux/get_alert.go

cmd/flux/get_alertprovider.go

cmd/flux/get_all.go

cmd/flux/get_receiver.go

cmd/flux/receiver.go

cmd/flux/reconcile.go

cmd/flux/reconcile_alert.go

cmd/flux/reconcile_alertprovider.go

cmd/flux/reconcile_receiver.go