Improve update experience in Discover
We created KDE Linux's [appstream description](https://invent.kde.org/kde-linux/kde-linux/-/merge_requests/136), and the rest of the pieces are still falling in place. See the documentation of the AppStream OS Component file: https://www.freedesktop.org/software/appstream/docs/sect-Metadata-OS.html
Now we need to polish up the UX of updating using Discover:
- [ ] https://invent.kde.org/plasma/discover/-/issues/41 - Poor feedback for large transactions
- [x] https://bugs.kde.org/show_bug.cgi?id=502041 - Updates shown as "0B" in size
- [ ] https://invent.kde.org/kde-linux/kde-linux/-/issues/164 - auto-generate better description of each update
- [ ] https://bugs.kde.org/show_bug.cgi?id=502042 - No licenses shown in update details
- [x] https://bugs.kde.org/show_bug.cgi?id=502040 - While updating, two identical transactions are shown on Tasks View
- [x] https://bugs.kde.org/show_bug.cgi?id=508556 - "Apply system update" setting is not relevant with sysupdate backend
- [x] https://bugs.kde.org/show_bug.cgi?id=502165 - Does not prompt for reboot after update downloads
- [x] https://bugs.kde.org/show_bug.cgi?id=501772 - After closing the window while updating, transaction progress notification displays mismatching counts
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