introduce a flag to enforce different types of behavior how to handle network peering implementation in lower levels

[balpert89]

Summary

The current behavior dictates metalnetlet will reflect peering information into lower level types, e.g. https://github.com/ironcore-dev/metalnet/blob/main/api/v1alpha1/network_types.go#L20-L29. If there are other implementors of peering instead of metalnet the solutions will get in conflict with each other.

This issue proposes the introduction of a new typed string, NetworkPeeringControllingType:

type NetworkPeeringControllingType string

const (
    NetworkPeeringControllingTypeNative = "Native"
    NetworkPeeringControllingTypeNone = "None"
)

If unset or "Native" is passed, the current behavior is kept in place, such as metalnetlet will populate the peered prefixes for the lowlevel Network resources.

If "None" is passed, metalnetlet will not populate any peered prefixes for the metalnet-related Network resources.

The behavior should be introduced with a commandline flag, such as --network-peering-controlling-behavior.