HA for application and applicationset controller

[sspreitzer]

Is your feature request related to a problem?

The helm chart (merely the HA specific documentation) does not yet cover the high-availability or scalability of the application- and applicationset-controller.

Related helm chart

argo-cd

Describe the solution you'd like

Implement and describe high availability of the application-/applicationset controller.
https://argo-cd.readthedocs.io/en/stable/operator-manual/high_availability/#argocd-application-controller

Describe alternatives you've considered

I did not consider an alternative, the topic is pretty straight forward.

Additional context

HA in general maybe needs to be re-validated due to the version 4 of the chart.

[github-actions]

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