Check if we can configure explicit certificates for argocd-operator kube-rbac-proxy

[simu]

kube-rbac-proxy v0.15.0 logs a deprecation warning during startup:

Insecure listen address will be removed.
Using --insecure-listen-address won't be possible!

The ability to run kube-rbac-proxy without TLS certificates will be removed.
Not using --tls-cert-file and --tls-private-key-file won't be possible!

For more information, please go to https://github.com/brancz/kube-rbac-proxy/issues/187

We should investigate whether we can configure the argocd-operator kube-rbac-proxy to use explicitly configured certificates. We most likely can't use cert-manager in component-argocd, since that would create a circular dependency which would break bootstrapping.

On OpenShift 4, we could use service serving certificates (cf. https://docs.openshift.com/container-platform/4.13/security/certificates/service-serving-certificate.html, but we don't have a similar solution for non-OCP4 (and the HackDay PoC currently depends on cert-manager, cf. https://github.com/projectsyn/k8s-service-ca-controller)

See also brancz/kube-rbac-proxy#187