reference material for charmhub containers-$charms

[kwmonroe]

Originally raised as: https://bugs.launchpad.net/charm-kubernetes-master/+bug/2043783

Users coming from ck8s < 1.24 may not be aware of the charm store -> charmhub migration and could find it unsettling that our primary charms are only supported on 1.24+.

We should call out the existence of ~containers charms that are archived versions of charm store charms in charmhub. E.g.:

cs:~containers/kubernetes-worker-838

can be found here:

https://charmhub.io/containers-kubernetes-worker

And note the juju refresh $foo --switch containers-$foo that may be needed to get people onto charmhub-native releases.

[evilnick]

If you want to add something I'm okay with it, but it is already covered in the specific upgrade docs - https://ubuntu.com/kubernetes/docs/1.24/upgrading, including the use of --switch
As the upgrade doc is the recommended procedure to follow, I'm not sure who else we need to tell?