Sync VCF file

I use Syncthing to sync my files, so I think it should be possible to sync my contacts with it as well. While I acknowledge that a CardDAV server is the recommend way, it introduces an additional step that doesn't need to be required if a file sync service is already available in theory.

It would be great to have this functionality by introducing persistent VCF storage by hooking into the events to modify the initial exported file after enabling this option (i.e. contact adding/editing/removing) as well as wiping and re-importing such file when its hash has changed.

Something along those lines. Thanks.