Improve user feedback when communicating that an unsupported version is available (server side)

[adamkpickering]

Currently a generic message ("Unsupported Update Available" IIRC) is displayed when Rancher Desktop receives info from Upgrade Responder that a newer version is available, but unsupported. We want to improve the user experience by providing info as to why a version is unsupported.

The best way to do this that I am aware of is to include a Reason field in each Rule in the Upgrade Responder config. This can then be passed to Rancher Desktop in the query response, and Rancher Desktop can display this message in the UI.

The client side issue for this is rancher-sandbox/rancher-desktop#4760.

See rancher-sandbox/rancher-desktop#3925 (comment) for some ideas.