sysupdate: Limit update to at most one major version

[Nils Kattenbeck]

> I'd be fine with adding MaxVersion=. Happy to review a patch, merge
> something like this (at least file an RFE issue)

Should that be inclusive or exclusive? Naming it MaxVersion would
imply it to be inclusive though an exclusive bound would likely be
more useful most of the time. One could then specify MaxVersion=1.3.0
in their 1.2.x images and once they have an upgrade path they would
explicitly raise the max version in e.g. 1.2.15. Otherwise they would
have to specify 1.99.99.
In retrospect a VersionBound= property with syntax similar to
ConditionKernelVersion= would have been better though I guess that
ship has sailed - or is it? Is sd-sysupdate still considered
experimental? Not sure if this warrants such a change though :shrug:

Should we continue this discussion on the mailing list or an issue?

Kind regards, Nils