Upgrade Bottlerocket node with explicit Version field

[yuxiang-zhang]

Description

Fixes #7627

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the userdocs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes
• (Core team) Added labels for change area (e.g. area/nodegroup) and kind (e.g. kind/improvement)

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[TiberiuGC]

Great catch spotting that Bottlerocket release version doesn't necessarily change with K8s version!

This inconsistency makes reasoning about nodegroup upgrades annoyingly complicated. The fix seems to work, but the code section as a whole feels hacky. I take the blame for not properly re-factoring it myself when previously working on a related issue.

I don't have a problem approving it as is, so that we un-block eksctl users, but we may want to consider adding a new ticket for refactoring this area. In general, make it easier to understand whether release version, K8s version or both are being upgraded, and why that is.

[TiberiuGC]

I think this log doesn't always reflect the reality, as you might upgrade to a release version corresponding to next K8s version (e.g. for AL2 images).

[yuxiang-zhang]

yeah I agree, any suggestions? how about something like will only use release version for upgrade

[TiberiuGC]

Maybe we can have two separate logs depending on which ngResource field is set.

if ngResource.ReleaseVersion == nil {
    logger.Info(fmt.Sprintf("will upgrade nodes to Kubernetes version: %s", ngResource.KubernetesVersion))
} else {
    logger.Info(fmt.Sprintf("will upgrade nodes to release version: %s", ngResource.ReleaseVersion))
}

Something along these lines, wdyt?