[OPENJDK-3634] update image name in jlink template

[Josh-Matsuoka]

Addresses https://issues.redhat.com/browse/OPENJDK-3634

Brings over the work done in 884c621 , Updates the image name in jlink template to reflect it's tech-preview status and the new name of the jlink container. Also bumps up the recommended/example JDK version to 21.

[jmtd]

see inline messages

[sefroberg]

We should not be over writing the existing ubi9-jdk21 image but adding a new file here. I don't see how what we are doing is going to save us any time or effort in the short, medium or long-term. In the long term, it will make attempting to merge this branch back into the UBI9 branch impossible.

[jmtd]

Hi @sefroberg

can you expand on what the problems are?

In the long term, it will make attempting to merge this branch back into the UBI9 branch impossible.

In the future if we are looking at merging jlink-dev down to ubi9, that is presumably because we are moving the feature from Tech Preview to GA. In which case, we'd want the changes in the main UBI9/21 image, rather than in a separate TP image, which would be going away at that point. We would need to revert the image name changes at that point, and make various other changes. But in either case the changes needed to the image YAML are tiny.

[jmtd]

Also to be clear the image changes are already merged, happy to have that discussion but this PR doesn't touch the image YAMLs.

[jmtd]

@Josh-Matsuoka I'm reviewing this now but please take a look at resolving merge conflicts: something has changed in jlink-dev since you forked for this. Thanks!

[jmtd]

LGTM (subject to resolving merge conflicts)