Detect when the VFS graph driver is used

[almet]

We've had issues opened on the repository where users are using the VFS storage driver (#993).

This driver is not meant to be used in production, and makes dangerzone fail. We should detect it is used and report it to the end user.

[almet]

vfs seem to be the default podman storage backend on debian bookworm, from what I understand.

Installing the containers-storage package seem to change the default backend to overlayfs2 so we might want to point this out.

[apyrgio]

I suppose you propose adding a runtime check for the vfs driver, right, perhaps as part of the instalation? I'd be in favor of that. What about suggesting a solution to our users. On Windows/macOS, it seems the issue was resolved once users reinstalled Docker Desktop. On Linux, we could ask them to create a .config/containers/storage.conf file with the proper driver. What do you think?