We should replace examples that contain hard-coded references to base image names with attributes.

This should ease the task of verifying the docs set to check for discrepancies between releases.
It will also help us keep track of image name changes more easily:

For example, code snippets such as:

oc import-image --confirm ubi8/openjdk-11 --from=registry.access.redhat.com/ubi8/openjdk-11

can be changed to:

oc import-image --confirm {name-image-ubi8-open-jdk-11-short} --from={{name-image-ubi8-open-jdk-11}

we'll need to add attributes in common/attributes.adoc:

:name-image-ubi8-open-jdk-11: registry.access.redhat.com/ubi8/openjdk-11
:name-image-ubi8-open-jdk-11-short: ubi8/openjdk-11

Additionally, attribute created for the Mandrel image:

:name-native-image-mandrel-java-11: registry.access.redhat.com/quarkus/mandrel-20-rhel8:20.3