Enhancement: Allow excluding online-only cloud files (e.g. OneDrive)

Restic treated files synced using OneDrive Files On-Demand as though they
were regular files. This caused issues with VSS and could cause OneDrive to
download all files.

Restic now allows the user to exclude these files when backing up with
the `--exclude-cloud-files` option.

https://github.com/restic/restic/issues/3697
https://github.com/restic/restic/issues/4935
https://github.com/restic/restic/pull/4990
