Protected containers: Use consistent actor when checking for feature flag :container_registry_protected_containers

Before starting roll out process for the feature flag :container_registry_protected_containers, we need to ensure that all checks regarding a feature flag use a consistent actor. This is also recommended by the feature flag guide line, see line The same actor type must be used consistently for all invocations of Feature.enabled?

This was pointed out by @10io in this comment.

Proposal

@10io also proposed that we can use the root namespace of project or group unify the different actor types, see here.