Description of problem:

When it's used UI to create a Kafka instance, the default CR suggestion does not work. It returns an error: "Required value" for field "spec.kafka.listeners". Here is the current CR:

apiVersion: kafka.strimzi.io/v1beta1
kind: Kafka
metadata:
  name: my-cluster
  labels: {}
  namespace: amq-streams
spec:
  kafka:
    config:
      offsets.topic.replication.factor: 3
      transaction.state.log.replication.factor: 3
      transaction.state.log.min.isr: 2
      log.message.format.version: '2.5'
    version: 2.5.0
    storage:
      type: ephemeral
    replicas: 3
  zookeeper:
    storage:
      type: ephemeral
    replicas: 3

The workaround is to add the required value as shown below:
apiVersion: kafka.strimzi.io/v1beta1
kind: Kafka
metadata:
  name: my-cluster
  labels: {}
  namespace: amq-streams
spec:
  kafka:
    config:
      offsets.topic.replication.factor: 3
      transaction.state.log.replication.factor: 3
      transaction.state.log.min.isr: 2
      log.message.format.version: '2.5'
    listeners:
      plain: {}
    version: 2.5.0
    storage:
      type: ephemeral
    replicas: 3
  zookeeper:
    storage:
      type: ephemeral
    replicas: 3

    listeners:
      plain: {}


Version-Release number of selected component (if applicable):
4.6.0-0.nightly-2020-07-04-234602
AMQ Streams 1.5.0

How reproducible:
Always

Steps to Reproduce:
1. Install AMQ Streams Operator
2. Create Kafka instance with default values


Actual results:
Kafka instance is failing due to a required field

Expected results:
Kafka should work with the default suggested CR