KafkaConnectResource.kafkaConnect(CLUSTER_NAME, 2)
                .editSpec()
                    .withNewRack()
                        .withTopologyKey(clientRackKey)
                    .endRack()
                    // kafka only line
                   .addToConfig("replica.selector.class", "org.apache.kafka.common.replica.RackAwareReplicaSelector")
                .endSpec().done();

oc get kc -n specific-cluster-test -o yaml
apiVersion: v1
items:
- apiVersion: kafka.strimzi.io/v1beta1
  kind: KafkaConnect
  metadata:
    creationTimestamp: "2020-11-02T11:11:47Z"
    generation: 1
    managedFields:
    ...
    name: my-cluster
    namespace: specific-cluster-test
    resourceVersion: "4439106"
    selfLink: /apis/kafka.strimzi.io/v1beta1/namespaces/specific-cluster-test/kafkaconnects/my-cluster
    uid: 3d1080b0-da11-4e4e-8c9e-06169900b34c
  spec:
    bootstrapServers: my-cluster-kafka-bootstrap:9093
    config:
      config.storage.topic: my-cluster-connect-config
      group.id: my-cluster-connect
      offset.storage.topic: my-cluster-connect-offsets
      replica.selector.class: org.apache.kafka.common.replica.RackAwareReplicaSelector
      status.storage.topic: my-cluster-connect-status
    logging:
      loggers:
        connect.root.logger.level: DEBUG
      type: inline
    rack:
      topologyKey: client-rack
    replicas: 2
    tls:
      trustedCertificates:
      - certificate: ca.crt
        secretName: my-cluster-cluster-ca-cert
    version: 2.6.0
  status:
    conditions:
    - lastTransitionTime: "2020-11-02T11:11:47.920491Z"
      message: 'Failure executing: PATCH at: https://172.30.0.1/apis/rbac.authorization.k8s.io/v1/clusterrolebindings/strimzi-specific-cluster-test-my-cluster-kafka-init. Message: clusterroles.rbac.authorization.k8s.io "strimzi-kafka-client" not found. Received status: Status(apiVersion=v1, code=404, details=StatusDetails(causes=[], group=rbac.authorization.k8s.io, kind=clusterroles, name=strimzi-kafka-client, retryAfterSeconds=null, uid=null, additionalProperties={}), kind=Status, message=clusterroles.rbac.authorization.k8s.io "strimzi-kafka-client" not found, metadata=ListMeta(_continue=null, remainingItemCount=null, resourceVersion=null, selfLink=null, additionalProperties={}), reason=NotFound, status=Failure, additionalProperties={}).'
      reason: KubernetesClientException
      status: "True"
      type: NotReady
    labelSelector: strimzi.io/cluster=my-cluster,strimzi.io/name=my-cluster-connect,strimzi.io/kind=KafkaConnect
    observedGeneration: 1
    replicas: 2
    url: http://my-cluster-connect-api.specific-cluster-test.svc:8083
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""