[FFe] plasma-distro-release-notifier for Ubuntu Studio and Kubuntu

plasma-distro-release-notifier is an applet which, in conjunction with update-notifier, notifies the user of a new version of Ubuntu using the same logic that update-notifier currently uses from the configuration in /etc/update-manager/release-upgrades. This has been sorely missing from previous releases of Ubuntu Studio and Kubuntu and should be included in all releases of Ubuntu Studio and Kubuntu going forward and should be included in currently supported releases.

Currently, users are not prompted when a new version of Ubuntu is released, and as such, users of the Plasma desktop (Ubuntu Studio and Kubuntu) get stuck on an EOL release very quickly. I have seen several posts on #kubuntu and Reddit requesting help because the user simply did not know that they needed to update their machine to a newer release. Including this package would prevent that.

Tests on 20.04 using the same package have been successful, with not only a notification, but also a tray icon indicating that the upgrade is available.

The intention will be, once through this FFe process, to backport the package via SRU to 22.04. A stretch goal would be to backport the same package to Kubuntu 20.04 through the same process as it is still supported until April 2023 and many users there are not getting the prompt to upgrade.

As of this writing, plasma-distro-release-notifier has been accepted into kinetic.