Add flag to automatically generate admission CA and server cert

[tsandall]

When kube-mgmt is deployed and automatically registers OPA as an admission controller, it would be nice if it would take care of generating the CA and server cert (and making the latter available to OPA) as this is currently done manually. This should be an optional feature that users can enable using a command line argument.

[gordonbondon]

Maybe you can leverage cert-manager here. They have a way to bootstrap certificates for webhooks and updating them in admission controller configuration: https://github.com/jetstack/cert-manager/blob/master/contrib/manifests/cert-manager/with-rbac-webhook.yaml

[eshepelyuk]

@tsandall it seems implemened in helm chart already, can this be closed ?