Update pkpass files from the web

[TheLastProject]

Pkpass files can be updated online: https://developer.apple.com/documentation/walletpasses/adding-a-web-service-to-update-passes

While the documentation suggests this is mostly for changes like boarding gate for plane travel, some organizations seem to use it to "expire" passes periodically, breaking them if you don't update them: https://mastodontech.de/@Smojo/113973063261105479

It should be possible to check for updates, perhaps even automatically on a schedule.

Extra care needs to be taken to try to not override user changes (if made), although a first version could perhaps just warn that it will override. Looking deeper into it should hopefully surface the complexity.