ImageConfig should allow multiple pull secrets

[jsanda]

What is missing?
The ImageConfig API is to provide image configuration defaults that are supplied in a ConfigMap that look like this:

apiVersion: v1
data:
  controller_manager_config.yaml: |
    apiVersion: config.k8ssandra.io/v1beta1
    kind: OperatorConfig
    metadata:
      name: operator-config
    health:
      healthProbeBindAddress: :8081
    metrics:
      bindAddress: 127.0.0.1:8080
    webhook:
      port: 9443
    leaderElection:
      leaderElect: true
      resourceName: b569adb7.cassandra.datastax.com
    disableWebhooks: false
    imageConfigFile: /configs/image_config.yaml
  image_config.yaml: |
    apiVersion: config.k8ssandra.io/v1beta1
    kind: ImageConfig
    metadata:
      name: image-config
    images:
      system-logger: "k8ssandra/system-logger:v1.10.0"
      config-builder: "datastax/cass-config-builder:1.0.4-ubi7"
      # cassandra:
      #   "4.0.0": "k8ssandra/cassandra-ubi:latest"
      # dse:
      #   "6.8.999": "datastax/dse-server-prototype:latest"
    # imageRegistry: "localhost:5000"
    # imagePullPolicy: Always
    # imagePullSecret:
    #   name: my-secret-pull-registry
    defaults:
      # Note, postfix is ignored if repository is not set
      cassandra:
        repository: "k8ssandra/cass-management-api"
      dse:
        repository: "datastax/dse-server"
        suffix: "-ubi7"
kind: ConfigMap
metadata:
  creationTimestamp: "2022-05-25T13:08:53Z"
  name: cass-operator-manager-config
  namespace: k8ssandra-operator
  resourceVersion: "1471"
  uid: 9b74d066-141f-4acc-ad8e-9a0ddbfc38b5

As explained in the Kubernetes docs you can specify multiple image pull secrets for a pod.

Why do we need it?
To be consistent we should support multiple pull secrets in the ImageConfig API.

Environment

• Cass Operator version:

  1.11.0

  **Anything else we need to know?**:

┆Issue is synchronized with this Jira Story by Unito
┆Issue Number: CASS-41