In general ovn-controller POD is deployed on the control plane by the ovn-operator to provide centralized dataplane networking functionalities like e.g. SNAT, port_forwarding, etc. That's why EnableChassisAsGateway is set to True by default in the ovn-controller CRD.

But (probably) all of those functinalities requires connectivity to the External network so some configuration of the NicMappings is required for that. It can't really be done with any sane defaults as this setting heavily depends on the hardware used by the customer.

So goal of this story is to:

1. Investigate if we really need ovn-controller pod to be deployed if it isn't connected to any external network (no NicMappings configured), maybe there is some other function for which it is/can be used with only connectivity to the tenant network,
2. If this ovn-controller is only really useful when connected to the external network, then update ovn-controller controller so that POD will not be started at all if there is no NicMappings provided.
3. Deprecate and eventually remove EnableChassisAsGateway option.