Docs should show/explain how to use Custom Images in the KieApp CR

The Deployment on Openshift Guide shows how to create a custom image both for KieServer and SmartRouter but it does not show how to configure the KieApp yaml resource to specify the custom image.

There is the following config:

image: rhpam-kieserver-rhel8-custom
 imageContext: extension-image
 imageTag: '1.0'

and thre is this other one:

build:
  extensionImageStreamTag: 'jboss-kie-postgresql-extension-openshift-image:5.0.0'
  extensionImageStreamTagNamespace: exter-ns-custom
  extensionImageInstallDir: /extensions

When to use one or the other? The doc should provide a sample and an explanation of each property as well.

1. 3.5. Creating custom images for KIE Server and Smart Router