[Podman] pasta (passt) draft integration patch and demo

Hi, I played around with Podman to integrate pasta (if you never heard of it: https://passt.top/passt/about/#pasta-pack-a-subtle-tap-abstraction -- pasta is functionally similar to slirp4netns but without the Slirpiness). I prepared a demo at: https://passt.top/passt/about/#pasta_2 (the one on the right) from the out-of-tree patch at: https://passt.top/passt/tree/contrib/podman/0001-libpod-Add-pasta-networking... Let me know if you have questions, comments, interest in it, etc. Thanks, -- Stefano