Release changes to use prefixed repositories

[burmanm]

What this PR does:
cr.k8ssandra.io prefix for all deployed images from k8ssandra/* and cr.dstx.io for all deployed images from datastax/*

Resulting image_config.yaml:

apiVersion: config.k8ssandra.io/v1beta1
kind: ImageConfig
metadata:
  name: image-config
images:
  system-logger: "cr.k8ssandra.io/k8ssandra/system-logger:latest"
  config-builder: "cr.dtsx.io/datastax/cass-config-builder:1.0-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: "cr.k8ssandra.io/k8ssandra/cass-management-api"
    suffix: "-ubi8"
  dse:
    repository: "cr.dtsx.io/datastax/dse-mgmtapi-6_8"
    suffix: "-ubi8"

Which issue(s) this PR fixes:
Fixes #479

Checklist

• Changes manually tested
• Automated Tests added/updated
• Documentation added/updated
• CHANGELOG.md updated (not required for documentation PRs)
• CLA Signed: DataStax CLA

[adejanovski]

Suggestion: You could remove this comment, it's unclear why it was kept here.