Last synchronized (or seen) time should be exposed on principal's apps

[jannfis]

On the principal, we should expose a timestamp of the last known connection of the agent which is the origin or destination for a given app. This could be as simple as an annotation on the app, or we might use on of the status fields.

[jannfis]

With the introduction of the resource proxy and cluster secrets, I think we can expose this through the cluster secret. It already has fields for these kinds of information, that are already being displayed in Argo CD.