Provide IUK to go from version n-2 to version n

According to #10478-note_3 this would be used by ~30% of our users during the first week of a release and ~15% over the full release cycle. So, if we managed to make IUKs easier to provide (maybe #6309 (closed) helped on this) we could consider this.

Maybe some interesting data to have would be to know how much this would cost (in additional working time, possible bugs, infrastructure, etc.).

Note that allowing people to skip IUKs by going directly from n-2 to n might also fill their system partition slower (#11627 (closed)).

Related issues

• Related to #10478 (closed)
• Related to #11627 (closed)
• Related to #8142 (closed)

Original created by @sajolida on 11857 (Redmine)