feat(containers): clarify next major early access wording

[joshtrichards]

• Resolves: #

Summary

Until we expose more versioning info to the templates adjust the logic, this should clarify the messaging a bit when we offer early access to a new major release prior to it being the default in AIO. Or at least that's the idea.

Changes:

• Clarify what the note is about in its heading
• Clarify it can be used to upgrade to the a not-yet-default major version
• Clarify that when using this "early access" feature, this must also be utilized to upgrade to new maintenance releases
• Tighten up some wording
• Tidy up some formatting

Checklist

• The PR was tested and verified that it works locally
• Or will be tested after merge on a dedicated test instance (available for maintainers)
• Sign-off message is added to all commits
• Tests (playwright if possible) are included
• Screenshots before/after for front-end changes
• Documentation has been updated or is not required
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone next added

AI (if applicable)

• The content of this PR was partly or fully generated using AI