applicationset controller should not clear argocd.argoproj.io/refresh annotation

[jessesuen]

Describe the bug

When refreshing an application, the appset-controller will blindly replace the Applications .metadata.annotations with the annotations specified in the template. This means it will also clear the argocd.argoproj.io/refresh annotation that gets set on the application during a refresh

This could lead to situations where the app-controller could miss the refresh request because the appset-controller had already deleted the annotation.

To Reproduce

1. create an appset that generates an application foo
2. scale down application controller
3. refresh application foo
4. the foo application will be considered refreshed even though app-controller was down

Expected behavior

ApplicationSet controller should not touch argocd.argoproj.io/refresh as this field should only be cleared by app-controller.

Version

Argo CD v2.4.*

[jessesuen]

The fix can be similar to what we do for notified.notifications.argoproj.io annotation, in that it is preserved when updating an app

https://github.com/argoproj/argo-cd/blob/master/applicationset/controllers/applicationset_controller.go#L530-L537

			// Preserve argo cd notifications state (https://github.com/argoproj/applicationset/issues/180)
			if state, exists := found.ObjectMeta.Annotations[NotifiedAnnotationKey]; exists {
				if generatedApp.Annotations == nil {
					generatedApp.Annotations = map[string]string{}
				}
				generatedApp.Annotations[NotifiedAnnotationKey] = state
			}
			found.ObjectMeta.Annotations = generatedApp.Annotations