Provide a non-destructive way to clean up debris on the filesystem

[g-suraj]

Feature request description

Related to https://github.com/containers/podman/issues/3799, it looks as though podman leaves layers and other stuff on the filesystem. This cannot be inspected (via podman system df) or cleaned (via podman system prune). You can however see this with

$ podman unshare du -sh /tmp/containers/suraj
128G /tmp/containers/suraj

The proposed solution in the aforementioned issue for tidying up inaccessible/leaked layers in /containers/storage/ is podman system reset. This seems like a pretty nuclear option that will affect any podman builds in progress. This results in platforms utilising podman build having to work a lot harder.

Suggest potential solution

It'd be ideal if podman system prune could delete all these "leaked" layers that are not currently in use.