Restructure controller (edl) pacakge

[wangkuiyi]

We need to rename some functions in the controller (to be renamed edl) package. The motivation comes from the current main function:

https://github.com/PaddlePaddle/cloud/blob/dcebcdf820d4a7aa13e815e75d3a17f705794ec1/go/cmd/autoscaler/autoscaler.go#L51-L59

	cluster := controller.NewCluster(clientset)

	as := controller.New(cluster,
		controller.WithMaxLoadDesired(*maxLoadDesired))

	controller, err := controller.NewController(client, clientset, as)
	if err != nil {
		panic(err)
	}

should be

ctl, err = edl.New(client, clientset, *maxLoadDesired)

as

1. we rename controller.NewController into edl.New,
2. rename controller.New into edl.newAutoscaler, which should be called by edl.New,
3. rename controller.NewCluster into edl.newCluster, which should be called by edl.New too.