Bump kr8s to 0.17 and Kubernetes supported versions

[jacobtomlinson]

In kr8s==0.17 you can now use new_class as part of a class constructor. This avoids the need to manually subclass APIObject and should lead to more error free code.

With kr8s==0.17 only Kubernetes >=1.28 is supported and I'm noticing some CI failures with Kubernetes 1.26 so taking this opportunity to bump the Kubernetes CI versions.

I've also replaced the use of api.get(Type.endpoint, ...) with Type.list(...) which is a little more readable.