fix: periodically detect and update cluster connection status

[chetan-rns]

Argo CD doesn't report connection errors on the cluster UI page unless the cache is invalidated (manually/periodically every 24 hours) or there is a sync error. This error is only updated during auto-sync if there is a new commit to sync. This PR adds a new field ConnectionStatus that gets updated whenever Argo CD fails to access the cluster. The ClusterInfoUpdater will periodically fetch this cluster info and update the cache.

The cluster cache will start a goroutine with a configurable interval that pings (calls the version API) the remote cluster and checks if the cluster is reachable. It only pings the remote cluster if it detects any watch errors in the cluster cache thereby avoiding unnecessary calls. The implementation can be found here: argoproj/gitops-engine#559

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