The feature should consist of:
1. an additional field, optional/omitempty and defaulted to an empty string, in the ClusterPodPlacementConfig, fallbackArchitecture, that can take values from the set

2. a logic in the pod placement controller code that uses the fallbackArchitecture if not empty when the circuit breaker stops retrying the inspection of the pods' images. See https://github.com/openshift/multiarch-tuning-operator/blob/main/controllers/podplacement/pod_reconciler.go#L135-L142
3. Related recorded events should be updated according to the feature so that users are informed about the repeated failures in the image inspection/setup of the node affinities and the fact we set the fallback one (or none if fallbackArchitecture is empty).

We should document this enhancement in https://github.com/openshift/multiarch-tuning-operator/tree/main/docs/enhancements