Generate a local RSS feed changelog on the image.

[castrojo]

Doing the changelogs at the build step still eludes us. That's not going to be easy. How about this in the meantime. When the system service updates the image run a

rpm-ostree db diff --changelogs

transform it RSS and then toss it in /usr/share/ublue-os/doc/changelog.rss or whatever. Then on desktop we can use any RSS reader as a changelog reader.

Is there a decky RSS plugin? Maybe that'll be a decent way of getting the changelogs in bazzite since we can't really use the built in steam thing anyway.

Also put flatpak, and then grab the git changelog from the repo so that we can present it in sections and covering all aspects of the system.

And it'll be the correct changelog for that specific machine too, that'd be awesome.