Add support for export and import snapshot to/from local directory

[fabionitto]

My use case would benefit from exporting and importing minimal snapshots from local directories. To make minimal impact, export should follow the same pattern for snapshot export to minio, that is:

draksetup snapshot export_local --name <NAME> --dir <DIR>

would save cfg.template install.json and disk.img to <DIR>/<NAME>

Similarly,
draksetup snapshot import_local --name <NAME> --dir <DIR>

would read from <DIR>/<NAME> and import the snapshot.

Implementation should be simply moving and coping vm-0 snapshot files, and import method would probably be the same as importing from minio (only different file origin)

With this feature, I can install vm-0 previously and create a snapshot on my storage disk. When replicating my drakvuf VM, I can just plug the disk with the snapshot and import from there.