Use rollout informer instead of API list

[jessesuen]

In service.go:

func (c *Controller) getRolloutsForService(service *corev1.Service) ([]*v1alpha1.Rollout, error) {
	allROs, err := c.rolloutsclientset.ArgoprojV1alpha1().Rollouts(service.Namespace).List(metav1.ListOptions{})
	if err != nil {
		return nil, err
	}

We should use the informer instead of list API

[dthomson25]

With this issue, we should investigate the code base and find other places that we can switch to informers in addition to the above example

[dthomson25]

After investigating the code, the only place we use the API instead of the rollout informer is at https://github.com/argoproj/argo-rollouts/blob/master/controller/replicaset.go#L35. In this case, we are required to use the API to get up to date information.