Updates tab should allow checking for updates offline
Currently when the computer is offline, the Updates tab shows a message "Go online to check for updates" and the "Check for updates" button is not clickable. However this is not correct since the flatpak plugin can check for app updates on USB drives, and the eos-updater plugin can check for OS updates on USB drives, which works offline.
Should we just make the Updates tab the same regardless of network connectivity, or is there a better option? Presumably the purpose of the feature is to help users who might not realize they're offline and aren't using the offline updates feature. Should we have an informational message saying there's no connectivity, but still allow checking for updates?