Do not overwrite custom changes on argocd-ssh-known-hosts-cm when upgrading

[simonszu]

Summary

I have noticed that an upgrade of ArgoCD overwrites the configmap argocd-ssh-known-hosts-cm. This is a bit inconvenient when one has made custom changes, e.g. adding a SSH key for a private repo.

Motivation

This behaviour adds a repetitive additional step for each upgrading. Since it isn't needed to overwrite the configmap on upgrade, this should be handled differently.

Proposal

For now, the upgrade manifest is the same as the install-from-scratch manifest. Maybe it would just be sufficient to provide an upgrade-manifest which does not apply any configmaps.