cmd/k8s-operator: configure HA Ingress replicas to share certs
Creates TLS certs Secret and RBAC that allows HA Ingress replicas
to read/write to the Secret.
Configures HA Ingress replicas to run in read-only mode.
Updates tailscale/corp#24795
Signed-off-by: Irbe Krumina <irbe@tailscale.com>