feat: stamp Queue shard status with availability zones

Resolves each shard topic's replica broker IDs (internal/kafka.Admin.
ReplicaBrokerIDs) to the topology.kubernetes.io/zone labels of the nodes
hosting those brokers (ZoneLocator), and writes the result into
ShardStatus.AvailabilityZones each reconcile. Uses mgr.GetAPIReader()
rather than the cached client for the Pod/Node lookups, since the cached
client would otherwise require cluster-wide list/watch RBAC on Pods just
to serve occasional point Gets.

internal/operator/fake_admin.go

@@ -51,6 +51,15 @@ func (f *fakeAdmin) ConsumerLag(_ context.Context, group, topic string) (int64,
 	return f.lag[group+"/"+topic], nil
 }
 
+func (f *fakeAdmin) ReplicaBrokerIDs(_ context.Context, topic string) ([]int32, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	if _, ok := f.topics[topic]; !ok {
+		return nil, nil
+	}
+	return []int32{0}, nil
+}
+
 func (f *fakeAdmin) setOffsetSum(topic string, v int64) {
 	f.mu.Lock()
 	defer f.mu.Unlock()